An overview of some of ikiwiki's features:
Rather than implement its own system for storing page histories etc, ikiwiki uses a real Revision Control System. This isn't (just) because we're lazy, it's because a real RCS is a good thing to have, and there are advantages to using one that are not possible with a standard wiki.
Ikiwiki can be run from a post-commit hook to update your wiki immediately whenever you commit a change using the RCS.
It's even possible to securely let anonymous users git push changes to the wiki.
Note that ikiwiki does not require a RCS to function. If you want to run a simple wiki without page history, it can do that too.
Ikiwiki is a wiki compiler; it builds a static website for your wiki, and updates it as pages are edited. It is fast and smart about updating a wiki, it only builds pages that have changed (and tracks things like creation of new pages and links that can indirectly cause a page to need a rebuild)
By default, pages in the wiki are written using the MarkDown format. Any page with a filename ending in ".mdwn" is converted from markdown to html by ikiwiki. Markdown understands text formatted as it would be in an email, and is quite smart about converting it to html. The only additional markup provided by ikiwiki on top of regular markdown is the WikiLink and the directive.
If you prefer to use some other markup language, ikiwiki allows others to easily be added by plugins. For example it also supports traditional WikiText formatted pages, pages written as pure HTML, or pages written in reStructuredText or Textile.
Ikiwiki also supports files of any other type, including plain text, images, etc. These are not converted to wiki pages, they are just copied unchanged by ikiwiki as it builds your wiki. So you can check in an image, program, or other special file and link to it from your wiki pages.
Ikiwiki can also aggregate external blogs, feeding them into the wiki. This can be used to create a Planet type site that aggregates interesting feeds.
You can also mix blogging with podcasting by dropping audio files where they will be picked up like blog posts. This will work for any files that you would care to syndicate.
Valid html and css
Ikiwiki ships with several ready to use themes.
Plugins can be used to add additional features to ikiwiki. The interface is quite flexible, allowing plugins to implement additional markup languages, register directives, provide a RCS backend, hook into CGI mode, and much more. Most of ikiwiki's features are actually provided by plugins.
The standard language for ikiwiki plugins is perl, but ikiwiki also supports external plugins: Standalone programs that can be written in any language and communicate with ikiwiki using XML RPC.
After rather a lot of fiddling, we think that ikiwiki correctly and fully supports utf8 everywhere.
The above are the core design goals and features of ikiwiki, but on that foundation a lot of other important features are added. Here is an incomplete list of some of them.
You can tag pages and use these tags in various ways. Tags will show up in the ways you'd expect, like at the bottom of pages, in blogs, and in RSS and Atom feeds.
Arbitrarily deep hierarchies of pages with fairly simple and useful LinkingRules
Automatically included on pages. Rather faster than eg MoinMoin and always there to help with navigation.
Since it uses a real RCS, ikiwiki takes advantage of its smart merging to avoid any conflicts when two people edit different parts of the same page at the same time. No annoying warnings about other editors, or locking, etc, instead the other person's changes will be automatically merged with yours when you commit.
In the rare cases where automatic merging fails due to the same part of a page being concurrently edited, regular commit conflict markers are shown in the file to resolve the conflict, so if you're already familiar with that there's no new commit marker syntax to learn.
RecentChanges, editing pages in a web browser
Nearly the definition of a wiki, although perhaps ikiwiki challenges how much of that web gunk a wiki really needs. These features are optional and can be enabled by enabling CGI and a Revision Control System.
Can optionally be configured to allow only registered users to edit pages.
User registration can be done using a web form, or ikiwiki can be configured to accept users authenticated with OpenID, or HTTP basic authentication, or other methods implemented via plugins.
Thanks to subpages, every page can easily and automatically have a /Discussion subpage. By default, these links are included in the templates for each page. If you prefer blog-style comments, that is available too.
Wiki admins can lock pages so that only other admins can edit them. Or a wiki can be set up to allow anyone to edit Discussion pages, but only registered users to edit other pages. These are just two possibilities, since page edit controls can be changed via plugins.
Well, sorta. Rather than implementing YA history browser, it can link toor the like to browse the history of a wiki page.
Ikiwiki can use the xapian search engine to add powerful full text search capabilities to your wiki.
The po plugin allows translating individual wiki pages using
Can be set up so that w3m can be used to browse a wiki and edit pages without using a web server.