Debian

Debian is a computer operating system (OS) composed entirely of software which is both free and open source (FOSS). Its primary form, Debian GNU/Linux, is a popular and influential Linux distribution. It is a multipurpose OS; it can be used as a desktop or server operating system.

Twitter

Twitter is a free social networking and micro-blogging service that allows users to send "updates" (or "tweets"; text-based posts, up to 140 characters long) to the Twitter web site, via the Twitter web site, short message service (SMS), instant messaging, or a third-party application such as Twitterrific or Facebook.
Updates are displayed on the user's profile page and instantly delivered to other users who have signed up to receive them. The sender can restrict delivery to those in his or her circle of friends (delivery to everyone is the default).

wiki

A wiki is a collection of web pages designed to enable anyone who accesses it to contribute or modify content, using a simplified markup language. Wikis are often used to create collaborative websites and to power community websites. The collaborative encyclopedia, Wikipedia, is one of the best-known wikis. Wikis are used in business to provide intranets and Knowledge Management systems.