EtherCalc: Multiplayer Spreadsheet
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This document provides an overview of the history and development of spreadsheet software, beginning with VisiCalc in 1979 and continuing through various iterations including EtherCalc, wikiCalc, SocialCalc, and Sheetnode. It discusses the goals and technical approaches of these different spreadsheet platforms, including making spreadsheets collaborative, web-based, and supporting large numbers of cells. The document also covers the use of spreadsheets on the OLPC project and integration with mesh networking capabilities. Overall it traces the evolution of spreadsheets from early desktop programs to modern web-based collaborative applications.
![wikiCalc Edit Flow
A1: 100
A2: =A1*2
POST /
ajaxsetcell=host:page:A1:300
wikicalc.pl
200 OK
<?xml version="1.0"?>
<root><![CDATA[
A1:v:300:300:right:1:1::
A2:f:600:A1*2:right:1:1::
]]></root>](https://image.slidesharecdn.com/ethercalc-en-120422134910-phpapp02/85/EtherCalc-Multiplayer-Spreadsheet-79-320.jpg)
EtherCalc: Multiplayer Spreadsheet
- 4. Time Limited Just Stories No Coding
- 5. Time Limited Just Stories Ideas No Coding
- 6. ethercalc.org ‣ npm install -g ethercalc ‣ ethercalc Please connect to: http://0:8000/ nodejs.org/#download
- 8. History
- 10. Harvard, 1977
- 11. Harvard, 1977
- 12. Harvard, 1977
- 13. Harvard, 1977
- 14. Harvard, 1977
- 15. Original Vision
- 16. Original Vision Alto Workstation
- 17. Original Vision Alto Calculator- Workstation Mouse
- 18. Original Vision Alto Calculator- Workstation Head-mounted Mouse Display
- 19. Original Vision Alto Calculator- Workstation Head-mounted Mouse Display
- 22. =SUM( ) 0
- 23. 10 =SUM( ) 10 0
- 24. 10 20 =SUM( ) 30 10 0
- 25. 10 20 30 =SUM( ) 60 30 10 0
- 26. 10 20 30 =SUM( ) 60 30 10 0
- 27. 1977 → 1978
- 28. 1977 → 1978
- 29. 1977 → 1978 + Integer BASIC
- 30. 1978 → 1979
- 31. 1978 → 1979 10 20 30 =SUM( ) 60
- 32. 1978 → 1979 A B C D 1 10 20 30 2 =SUM( ) 60
- 33. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60
- 34. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60 Bob & Dan
- 35. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60 ‣ Dan prototypes in BASIC Bob & Dan
- 36. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60 ‣ Dan prototypes in BASIC ‣ Bob codes in 6502 ASM Bob & Dan
- 37. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60 ‣ Dan prototypes in BASIC ‣ Bob codes in 6502 ASM ‣ 700,000 copies in 6 years Bob & Dan
- 38. 1978 → 1979 A B C D 1 10 20 30 2 =SUM(A1,B1,C1) 60 ‣ Dan prototypes in BASIC ‣ Bob codes in 6502 ASM ‣ 700,000 copies in 6 years ‣ The !rst “Killer App” Bob & Dan
- 39. 1981
- 45. 20 years passed
- 46. 20 years passed
- 47. 20 years passed
- 48. 20 years passed
- 49. 20 years passed Nothing changed
- 51. “Can’t open”
- 55. Wikipedia, 2001
- 56. Wikipedia, 2001
- 57. Wikipedia, 2001
- 58. wikiCalc, 2005
- 59. wikiCalc, 2005 ✓ Plain text, HTML & Wiki syntax
- 60. wikiCalc, 2005 ✓ Plain text, HTML & Wiki syntax ✓ References cells on other servers
- 61. wikiCalc, 2005 ✓ Plain text, HTML & Wiki syntax ✓ References cells on other servers ✓ Keeps all operations for auditing
- 62. wikiCalc, 2005 ✓ Plain text, HTML & Wiki syntax ✓ References cells on other servers ✓ Keeps all operations for auditing ✓ Revert to any revision
- 63. wikiCalc, 2005 ✓ Plain text, HTML & Wiki syntax ✓ References cells on other servers ✓ Keeps all operations for auditing ✓ Revert to any revision ✓ Open Source! (GPLv2)
- 64. wikiCalc.pl
- 65. wikiCalc.pl 網站 Sites ./wkcdata/sites/Foo ./wkcdata/sites/Bar ./wkcdata/sites/Baz
- 66. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ
- 67. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格
- 68. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100
- 69. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 A2: =A1*2
- 70. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 B1: =XXX!C1 A2: =A1*2
- 71. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 B1: =XXX!C1 A2: =A1*2
- 72. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 B1: =XXX!C1 A2: =A1*2 B2: =YYY!D2
- 73. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 B1: =XXX!C1 A2: =A1*2 B2: =YYY!D2
- 74. wikiCalc.pl 網站 Sites 頁面 Pages ./wkcdata/sites/Foo XXX ./wkcdata/sites/Bar ./wkcdata/sites/Baz YYY ZZZ Cells 儲存格 A1: 100 B1: =XXX!C1 A2: =A1*2 B2: =YYY!D2 Cross-page Reference
- 76. wikiCalc Edit Flow A1: 100 A2: =A1*2
- 77. wikiCalc Edit Flow A1: 100 A2: =A1*2
- 78. wikiCalc Edit Flow A1: 100 A2: =A1*2 POST / ajaxsetcell=host:page:A1:300 wikicalc.pl
- 79. wikiCalc Edit Flow A1: 100 A2: =A1*2 POST / ajaxsetcell=host:page:A1:300 wikicalc.pl 200 OK <?xml version="1.0"?> <root><![CDATA[ A1:v:300:300:right:1:1:: A2:f:600:A1*2:right:1:1:: ]]></root>
- 80. “Loading…”
- 81. “Loading…”
- 85. Undo
- 86. Undo Redo
- 87. SocialCalc, 2006 Dan Bricklin Ross Mayfield
- 88. Design Goals
- 89. Design Goals ‣ Rewrite calc engine in JS
- 90. Design Goals ‣ Rewrite calc engine in JS ‣ Real-time responsive editor
- 91. Design Goals ‣ Rewrite calc engine in JS ‣ Real-time responsive editor ‣ Supports 100,000+ cells
- 92. Design Goals ‣ Rewrite calc engine in JS ‣ Real-time responsive editor ‣ Supports 100,000+ cells ‣ Works on all browsers (IE6+)
- 93. Design Goals ‣ Rewrite calc engine in JS ‣ Real-time responsive editor ‣ Supports 100,000+ cells ‣ Works on all browsers (IE6+) ‣ Client-side log & undo/redo
- 94. Architecture
- 96. Architecture SocialCalc.js GET HTTP Server
- 97. Architecture SocialCalc.js GET HTTP Server
- 98. Architecture SocialCalc.js GET GET HTTP Server
- 99. Architecture SocialCalc.js GET GET ($) HTTP Server
- 100. Architecture SocialCalc.js PUT GET GET ($) HTTP Server
- 101. Architecture SocialCalc.js PUT GET GET ($) HTTP Server
- 102. Command Pattern
- 103. Command Pattern set A1 value n 42
- 104. Command Pattern set A1 value n 42 set A2 formula A1*2
- 105. Command Pattern set A1 value n 42 set A2 formula A1*2 merge A1:B2 cut A3 paste A4 sort A1:B9 A up B down set sheet defaultcolor blue ...
- 106. Command Pattern set A1 value n 42 set A2 formula A1*2 ‣ Async recalc loop
- 107. Command Pattern set A1 value n 42 set A2 formula A1*2 ‣ Async recalc loop ‣ Visible-only redraw
- 108. Command Pattern set A1 value n 42 set A2 formula A1*2 ‣ Async recalc loop ‣ Visible-only redraw ‣ Unlimited undo/redo
- 109. Command Pattern set A1 value n 42 set A2 formula A1*2 ‣ Async recalc loop ‣ Visible-only redraw ‣ Unlimited undo/redo ‣ UI stays responsive
- 110. Command Pattern set A1 value n 42 set A2 formula A1*2 ‣ Async recalc loop ‣ Visible-only redraw ‣ Unlimited undo/redo ‣ UI stays responsive
- 111. “Social”Calc
- 112. “Social”Calc
- 113. “Social”Calc Comment, Like, Tag, Share, Embed...
- 114. Objects Relations
- 115. Objects Relations
- 116. Objects Relations
- 120. Common Public Attribution License ⓐ BSD, MIT
- 121. Common Public Attribution License © ⓐ BSD, MIT LGPL, MPL
- 122. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL
- 123. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 124. loophole”
- 125. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 126. loophole” Affero GPL
- 127. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 128. loophole” CPAL Affero GPL
- 129. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 130. loophole” CPAL Affero GPL
- 131. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 132. loophole” CPAL Affero GPL
- 133. Common Public Attribution License © ++© ⓐ BSD, MIT LGPL, MPL GPL “ASP
- 134. loophole” CPAL Affero GPL
- 136. Sheetnode, 2008 Views + Fields + CCK Karim Ratib
- 137. Sheetnode, 2008 Views + Fields + CCK SocialCalc.js Karim Ratib
- 138. Sheetnode, 2008 Views + Fields + CCK SocialCalc.js Karim Ratib
- 139. Sheetnode, 2008 Views + Fields + CCK SocialCalc.js Karim Ratib
- 140. Sheetnode, 2008 Views + Fields + CCK SocialCalc.js Karim Ratib
- 141. OLPC, 2008
- 142. OLPC, 2008 Luke Closs Dan
- 145. Mesh P2P
- 147. Manusheel Gupta Vijit Singh
- 148. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js XoCom.py Manusheel Gupta Vijit Singh
- 149. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js set A1 value n 42 XoCom.py Manusheel Gupta Vijit Singh
- 150. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js set A1 value n 42 XoCom.py D-Bus + Telepathy Manusheel Gupta Vijit Singh
- 151. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js set A1 value n 42 XoCom.py D-Bus + Telepathy OLPC Mesh Manusheel Gupta Broadcast 網絡廣播 Vijit Singh
- 152. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js set A1 value n 42 XoCom.py D-Bus + Telepathy OLPC Mesh Manusheel Gupta Broadcast 網絡廣播 D-Bus + Telepathy Gecko/XPCOM SocialCalc.js XoCom.js XoCom.py Vijit Singh SocialCalcActivity.py
- 153. SocialCalcActivity.py Gecko/XPCOM SocialCalc.js XoCom.js set A1 value n 42 XoCom.py D-Bus + Telepathy OLPC Mesh Manusheel Gupta Broadcast 網絡廣播 D-Bus + Telepathy Gecko/XPCOM set A1 value n 42 SocialCalc.js XoCom.js XoCom.py Vijit Singh SocialCalcActivity.py
- 154. Great, but...
- 155. Great, but... ‣ Must log on same time
- 156. Great, but... ‣ Must log on same time ‣ Can’t replay missed logs
- 157. Great, but... ‣ Must log on same time ‣ Can’t replay missed logs ‣ Race condition on cells
- 158. Great, but... ‣ Must log on same time ‣ Can’t replay missed logs ‣ Race condition on cells ‣ OLPC-specific code!
- 159. YAPC::Tiny, 2009 跳格 Multiplayer SocialCalc 二零零九 唐鳳 字 中英雙宇有字版
- 160. EV/AnyEvent
- 162. Tatsumaki EV/AnyEvent Web::Hippie @miyagawa @clkao
- 163. Tatsumaki EV/AnyEvent Web::Hippie Feersum @miyagawa @clkao @stash
- 164. WebSocket Channels multiserver.pl Web::Hippie Plack Feersum EV/libev
- 165. WebSocket Channels SpreadsheetControl multiserver.pl Web::Hippie ScheduleScheetCommand set A1 value n 2046 Plack RenderSheet Feersum EV/libev
- 166. WebSocket Channels SpreadsheetControl multiserver.pl Web::Hippie ScheduleScheetCommand set A1 value n 2046 Plack RenderSheet Send Feersum EV/libev
- 167. WebSocket Channels SpreadsheetControl multiserver.pl ScheduleScheetCommand Web::Hippie Relay set A1 value n 2046 Plack RenderSheet Send Feersum EV/libev
- 168. WebSocket Channels SpreadsheetControl multiserver.pl ScheduleScheetCommand Web::Hippie Relay set A1 value n 2046 Plack ScheduleScheetCommand RenderSheet Send Feersum set A1 value n 2046 (isRemote = true) EV/libev RenderSheet
- 169. New Features
- 170. New Features ✓ Fetch logs on join
- 171. New Features ✓ Fetch logs on join ✓ Reconnection recovery
- 172. New Features ✓ Fetch logs on join ✓ Reconnection recovery ✓ Show peer cursors
- 173. New Features ✓ Fetch logs on join ✓ Reconnection recovery ✓ Show peer cursors ✓ Cross-browser support!
- 174. New Features ✓ Fetch logs on join ✓ Reconnection recovery ✓ Show peer cursors ✓ Cross-browser support!
- 175. Much better, but...
- 176. Much better, but... ‣ Which peer’s log to take?
- 177. Much better, but... ‣ Which peer’s log to take? ‣ What if everyone leaves?
- 178. Much better, but... ‣ Which peer’s log to take? ‣ What if everyone leaves? ‣ Who would keep the logs?
- 179. Much better, but... ‣ Which peer’s log to take? ‣ What if everyone leaves? ‣ Who would keep the logs? ‣ Replay 1,000+ commands?
- 180. Much better, but... ‣ Which peer’s log to take? ‣ What if everyone leaves? ‣ Who would keep the logs? ‣ Replay 1,000+ commands?
- 182. Undo
- 183. Undo Redo?
- 184. YAPC::NA, 2006
- 185. YAPC::NA, 2006 “I think, but I cannot prove, that by the next year JavaScript 2.0 will bootstrap itself, complete self hosting, compile back to JavaScript, and replace Ruby as the Next Big Thing in all environments. ”
- 186. YAPC::NA, 2006
- 187. YAPC::NA, 2006 “JavaScript will become the common backend for all dynamic languages, and so you can write Perl to run in the browser, on the server, and inside databases, all with the same set of development tools. ”
- 188. YAPC::NA, 2006
- 189. YAPC::NA, 2006 “Because, as we all know, worse is better, so the worst scripting language is doomed to become the best.”
- 190. YAPC::NA, 2006 “Because, as we all know, worse is better, so the worst scripting language is doomed to become the best.” 劣=夯
- 194. JavaScript: Good Part Only
- 195. CoeeScript: HalfPart Noise JavaScript: Good the Only cs = (js) = js/2 Jeremy Ashkenas
- 196. CoeeScript: HalfPart Noise JavaScript: Good the Only cs = (js) = js/2 Jeremy Ashkenas
- 197. CoeeScript: HalfPart Noise JavaScript: Good the Only cs = (js) = js/2 “Original JavaScript: 22k LOC. Ported to CoffeeScript: 5k LOC. {async, jsdom, zappa, optimist etc}++” Jeremy Ashkenas
- 199. {x,y} = @offset
- 200. {x,y} = @offset var _ref = this.offset;
- 201. {x,y} = @offset var _ref = this.offset; var x = _ref.x;
- 202. {x,y} = @offset var _ref = this.offset; var x = _ref.x; var y = _ref.y;
- 203. {x,y} = @offset var _ref = this.offset; var x = _ref.x; var y = _ref.y; js2coffee.org
- 207. Function::ᵒ = (fun) -
- 208. Function::ᵒ = (fun) - (arg) = @ fun arg
- 209. Function::ᵒ = (fun) - (arg) = @ fun arg f = (x) = x * 2
- 210. Function::ᵒ = (fun) - (arg) = @ fun arg f = (x) = x * 2 g = (x) = x * 3
- 211. Function::ᵒ = (fun) - (arg) = @ fun arg f = (x) = x * 2 g = (x) = x * 3 h = f .ᵒ g
- 212. Function::ᵒ = (fun) - (arg) = @ fun arg f = (x) = x * 2 g = (x) = x * 3 h = f .ᵒ g h 100 # 600
- 213. Function::ᵒ = (fun) - (arg) = @ fun arg f = (x) = x * 2 g = (x) = x * 3 h = f .ᵒ g h 100 # 600
- 214. Zappa: Lazy Node.js zappajs.org
- 215. Zappa: Lazy Node.js Maurice Machado zappajs.org
- 216. Zappa: Lazy Node.js “If you can describe it in 495 characters, why on earth should Maurice it take 879?” Machado zappajs.org
- 217. require('zappa') - @view layout: - html = body = @body @get '/': - @render 'index' @view index: - for name, value of { wiki: Wiki to HTML html: HTML to Wiki } form method: 'post', = p = textarea {name} p = input {type: 'submit', value}
- 218. require('zappa') - @view layout: - html = body = @body @get '/': - @render 'index' @view index: - for name, value of { wiki: Wiki to HTML html: HTML to Wiki } form method: 'post', = p = textarea {name} p = input {type: 'submit', value}
- 219. require('zappa') - @post '/': - - @view layout: if @data.wiki? @body html = body = @send w2h @data.wiki @get '/': - @render 'index' else if @data.html? @send h2w @data.html @view index: - for name, value of { else redirect '/' wiki: Wiki to HTML html: HTML to Wiki } form method: 'post', = p = textarea {name} p = input {type: 'submit', value}
- 220. COSCUP, 2011
- 221. COSCUP, 2011
- 222. COSCUP, 2011 hack
- 223. hack
- 224. hack
- 225. ...
- 226. COSCUP, 2011 hack
- 227. hack
- 228. hack
- 229. ...
- 230. EtherCalc Edit Flow
- 231. EtherCalc Edit Flow main.coffee sc.coffee Socket.io SocialCalc.js Express Node.js db.coffee EV/libuv redis.js Zappa
- 232. EtherCalc Edit Flow main.coffee sc.coffee Socket.io SocialCalc.js Express Node.js db.coffee EV/libuv redis.js Zappa Redis (optional)
- 233. EtherCalc Edit Flow main.coffee sc.coffee Socket.io SocialCalc.js Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js Redis (optional)
- 234. EtherCalc Edit Flow main.coffee MULTI sc.coffee GET snapshot Socket.io LRANGE log SocialCalc.js EXEC Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js Redis (optional)
- 235. EtherCalc Edit Flow main.coffee MULTI sc.coffee GET snapshot Socket.io LRANGE log SocialCalc.js EXEC Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js RPUSH log cmd Redis (optional)
- 236. EtherCalc Edit Flow main.coffee MULTI sc.coffee GET snapshot Socket.io LRANGE log SocialCalc.js EXEC Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js RPUSH log cmd Redis (optional)
- 237. EtherCalc Edit Flow main.coffee MULTI sc.coffee GET snapshot Socket.io LRANGE log SocialCalc.js EXEC Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js RPUSH log cmd Redis (optional)
- 238. EtherCalc Edit Flow main.coffee MULTI sc.coffee GET snapshot Socket.io LRANGE log SocialCalc.js EXEC Express Node.js db.coffee EV/libuv player.coffee redis.js Zappa SocialCalc.js MULTI RPUSH log cmd Redis DEL log (optional) SET snapshot snapshot EXEC
- 239. Recalc Subscription
- 240. Recalc Subscription
- 241. Recalc Subscription
- 242. Recalc Subscription ask.log: Foo
- 243. Recalc Subscription ask.log: Foo log: Foo,snapshot,log
- 244. Recalc Subscription ask.log: Foo log: Foo,snapshot,log execute: set A1 formula Bar!B2
- 245. Recalc Subscription ask.log: Foo log: Foo,snapshot,log execute: set A1 formula Bar!B2 ask.recalc: Bar
- 246. Recalc Subscription ask.log: Foo log: Foo,snapshot,log execute: set A1 formula Bar!B2 ask.recalc: Bar recalc: Bar,snapshot
- 247. Recalc Subscription ask.log: Foo log: Foo,snapshot,log execute: set A1 formula Bar!B2 ask.recalc: Bar recalc: Bar,snapshot recalc: Bar,snapshot
- 248. PaaS Deployment
- 249. PaaS Deployment stackato.yml app.js
- 250. PaaS Deployment stackato.yml app.js dotcloud.yml server.js
- 251. PaaS Deployment stackato.yml app.js dotcloud.yml server.js server.js
- 252. REST Interface
- 253. REST Interface GET /_/page PUT /_/page
- 254. REST Interface GET /_/page POST /_/page PUT /_/page {command:[…]}
- 255. REST Interface GET /_/page POST /_/page PUT /_/page {command:[…]} GET /_/page/cells/A1 PUT /_/page/cells/A1 GET /_/page/names/range
- 256. TODO, 2012
- 257. TODO, 2012 ‣ Chat EtherPad Lite
- 258. TODO, 2012 ‣ Chat EtherPad Lite ‣ Export/Import, Charts
- 259. TODO, 2012 ‣ Chat EtherPad Lite ‣ Export/Import, Charts ‣ Drupal Integration
- 260. TODO, 2012 ‣ Chat EtherPad Lite ‣ Export/Import, Charts ‣ Drupal Integration ‣ Socialtext Integration
- 261. TODO, 2012 ‣ Chat EtherPad Lite ‣ Export/Import, Charts ‣ Drupal Integration ‣ Socialtext Integration ‣ Forks welcome!
- 262. Thank you! EtherCalc Multiplayer Spreadsheet
- 263. EtherCalc The person who associated a work with this document has dedicated the work to the Commons by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law. Works under CC0 do not require attribution. ethercalc.tw