TikiWiki is not just a wiki engine, but wiki is one of its main features, along with forums, articles, image/file galleries and a lot more.
But as just a wiki, it complies with most of the points of your evaluation criterias:
- Installation: is easier as superuser, but doable for non-privileged users too (there is a doc in the site on how to install it in ftp-only access sites). It uses mysql, postgres, oracle, etc databases, and there are some recipes for prefixing the tables. But installation is not as trivial as other wiki engines, and still have some high space requirements for full installation
- Version control: it have versioning of wiki pages, and see differences between any two versions of a page (at least in 1.9 version, in previous you can see the diff between any version and the last one)
- Markup: Maybe is not as rich at it could be the TWiki one, but is powerful enough, and you can enable the html tags entry, and you can improve it a bit more with plugins.
- Attachments: yes, it supports file/image attachments, and with plugins even some integration with other Tikiwiki features.
- User and permissions: support groups of users (an user can belong to several groups even), and fine-grained permissions for that groups (i.e. a certain group can edit wiki pages, another can rename, and a wiki page can only be seen another one).
- Third-party extensions: plugins are the clasical extension that can be easily provided/programmed. There next version (in cvs right now) will have a repository for dinamically installable extensions,
- Internationalization and Localisation: You can select the charset of wiki page names, from english-only charset to full utf-8 chars names. You can also have languages attached to wiki pages and show your user's language version of the wiki page.
- Unique features: user management/permissions, Illustrations (ok, exist a sort of it with i.e. a TWiki plugin), and the other non-wiki features of the program (if i just need wiki is ok, but what about nested comments on pages? and full forums? file/image galleries? slashdot-like articles? "etc?" and all with the same user base/integrated permissions?).