Some interesting ideas from [TinyWiki:ActiveWikiPages]'s implementation section:
Some applications of this have cropped up. I'm seeing it used to armour email addresses by entity encoding them, to change TinyWiki's idea of the base document so that streetches of cut and paste Wiki markup continue to link to where they're from, and as a simple news blogger. I have my Wiki''Footer hacked to record HTTP Referer (sic) information in the itself, automatically linking back to anywhere that links to ie. Unanticipated uses rule.
PhpWiki has plugins you can embed into a wiki page. It's not really a scripting facility but as it defines a "safe mode" to run server side scripts, it might be quite easy to implement a kind of "script" plugin where a user would be able to enter server side script as an argument. I'll try to code such a plugin ... -- ArnaudFontaine
The interpreter is currently only a toy, but if ready probably portable to other languages (Perl at least) - and with a standard set of wiki.* functions, it could eventually allow for Wiki implementation independent and exchangeable feature plugins. (An idea discussed in the WikiFeatures wiki.)
See also ExtensibleWikis