An interesting set of communication systems recently gaining momentum with wider audiences are wikis. In essence, wikis, also categorized as social software, are web-based shared authoring environments. The concept of wikis was first invented by Ward Cunningham in 1995.
Aside from possible refinements to the features exposed by a wiki server (such as access control), all the content stored in the wiki is editable by all. Wikis use a simplified syntax to avoid requiring HTML authoring skills from their users, while allowing them to create links across pages on the same wiki, insert links to external documents or other wikis, or perform minimal formatting (typically bold or italic text, tables, lists).
The server or wiki container automatically exposes key shared authoring features: each page has a button to allow viewers to edit it (the full source is then shown in a text field and anyone can make changes to the entire page), another to display the history or the page (various wiki implementations either ship with their own diff tool or leverage the operating system’s tool). From anywhere in the wiki, a link is present to view the set of recent changes to the entire wiki, and thus allows the community to roll-back errors, to monitor the evolution of the content it shares.
This content is typically heavily linked, with a number of Starting points that are displayed as link on the top level page of the wiki. Not only can anyone edit each page, but anyone can also add new pages, restructure the organization of the pages and their linking, etc.
Most wikis I have played with are very bland in appearance. The simplicity of the syntax ensures a consistency in the look-and-feel of the knowledge base, but only at the cost of losing much of the formatting now expected by most readers. Even in the context of a wiki storing knowledge centered on technical documents, being stuck with a rather raw end-result is very constraining.
In addition, the co-authoring features are also very flat, with no inline mechanism where comments can be made, nor any mechanism allowing a review of the changes before they are promoted as the main version of the page.
But beyond these implementation limitations, the concept of almost-free-form, web-based co-authoring of a collection of pages constituting a shared knowledge base that keeps evolving with very little process constraints is very appealing.
For interesting examples of live, public wikis, take a look at the original wiki, or the wikipedia, a large-scale wiki-based encyclopedia.