Communication in an open-source community takes many forms, but all of these break down into two broad categories: synchronous (live/concurrent) and asynchronous (non-simultaneous). Synchronous communications might include instant messaging and various forms of audio chat; asynchronous communications include everything from email to wiki pages. Due to the geographically-dispersed nature of most communities, most communication makes heavy use of technology: it's no accident that open source in its current form has grown hand-in-hand with the Internet.
The online anchor-point for most communities is a web site. However, the nature of traditional HTML pages is that they are a static, one-to-many form of communication created by a small number of people with write access to a server. This leads to pages that can become quickly outdated and which do not truly reflect the collaborative nature of the community.
For this reason, many open source projects have an anchor site with a few static pages, but the bulk of their web content comes from wiki (user-editable), forum (user-posted), and mailing list archive pages.
The concept of a wiki is widely understood due to the popularity of Wikipedia: it's a web site where the pages are user-editable. A wiki provides an easy-to-use, asynchronous way of putting semi-permanent content on the web, so they are ideal for documentation, timelines, status reports, meeting minutes, and conversation logs. From the perspective of a reader, accessing wiki content is the same as accessing static HTML content, and search enginesindex wiki content very well. For the writer, a wiki provides version control, a database backend, simplified markup, and a fast edit-and-post cycle.
Most open source projects use one of the common wiki packages such as MediaWiki (which also powers Wikipedia), TikiWiki, MindTouch, or Trac; this has the benefit of reducing the number of different types of markup that must be memorized.
Wikis are related to content management systems (CMS), such as Drupal or Wordpress. When a project uses a CMS for a website, the goal is the same -- enable the community to edit the project content.
