This document discusses application wikis and their ability to provide high productivity for both developers and end users. It describes what wikis were in 1999 as "the simplest online database that could possibly work" and what they have become in 2009 with features like WYSIWYG editing, enterprise integration, structured and unstructured data, and being extensible platforms. It provides examples of use cases wikis are good for, like document-centric collaborative apps, and why developers and users appreciate wikis' out-of-the-box functionality. Finally, it outlines potential future directions for app wikis like annotations, real-time collaboration, peer-to-peer access, offline use, mobile access, and semantic capabilities.