I am looking for a wiki engine that is:
- open source
- real time
- collaborative
A sort of mix between MediaWiki and an open source version of Google Docs where several users could see each other's edits in real time.
Is there such a state-of-the-art beast?
I think you've answered this primarily - Google Wave or Google Docs are the big players here, though there's lots of others.
From a wiki perspective, most wiki's are written with the expectation of relatively non-granular changes (larger chunks than is typically found in collaboration). It may not be out there, and just waiting for someone like you to write it ;)