Wiki has turned out to be much more than I'd imagined! That is not to say that I didn't imagine a lot. These are the design principles I sought to satisfy with the first release of Wiki. -- WardCunningham
Note that this page is only a reconstruction from memory of intentions I held at the beginning. Additional principles, like server robustness, have been forced upon me.
Simple - easier to use than abuse. A wiki that reinvents HTML markup ([b]bold[/b], for example) has lost the path!
Open - Should a page be found to be incomplete or poorly organized, any reader can edit it as they see fit.
Incremental - Pages can cite other pages, including pages that have not been written yet.
Organic - The structure and text content of the site are open to editing and evolution.
Mundane - A small number of (irregular) text conventions will provide access to the most useful page markup.
Universal - The mechanisms of editing and organizing are the same as those of writing, so that any writer is automatically an editor and organizer.
Overt - The formatted (and printed) output will suggest the input required to reproduce it.
Unified - Page names will be drawn from a flat space so that no additional context is required to interpret them.
Precise - Pages will be titled with sufficient precision to avoid most name clashes, typically by forming noun phrases.
Tolerant - Interpretable (even if undesirable) behavior is preferred to error messages.
Observable - Activity within the site can be watched and reviewed by any other visitor to the site.
Convergent - Duplication can be discouraged or removed by finding and citing similar or related content.
There are many Wiki authors and implementers. Here are some additional principles that guide them, but were not of primary concern to me.
Trust - This is the most important thing in a wiki. Trust the people, trust the process, enable trust-building. Everyone controls and checks the content. Wiki relies on the assumption that most readers have good intentions. But see: AssumeGoodFaithLimitations
Fun - Everybody can contribute; nobody has to.
Sharing - of information, knowledge, experience, ideas, views...
Interaction - This enables guest interaction.
Collaboration - We believe that this could make a good collaboration tool, both synchronously and asynchronously.
Platforms - We like the cross-platform implications.
Social Networks - Its power for supporting collaboration is great.
See: WikiWikiHyperCard, WikiHistory.
In the list above Unified and Precise are the least generic and convincing points, especially if one thinks of how they apply to non-English wikis or to other engines like MediaWiki. Perhaps they can be reformulated as sub-points of Convergent? Cf. its opposite: «MeatBall:ViewPoint is nothing like a wiki».