1. Openstack is an open source cloud computing platform for both public and private clouds. It is made up of independent services for computing, storage, networking, identity etc.
2. Some of the main Openstack projects include Nova (compute), Swift (object storage), Cinder (block storage), Glance (images), Keystone (identity), and Neutron (networking). Newer projects provide additional capabilities like monitoring, orchestration, databases and messaging queues as services.
3. Openstack is used both in public clouds and by many private companies in their own data centers for infrastructure as a service capabilities. Contributors can get involved by joining the community and submitting code through the Openstack development process.