I know nothing about Everything. But I worked on twiki a fair bit (3000 page site, 300 users). The things I like about it are:

• it is a very rich wiki implementation
• it is written in comprehensible perl
• the twiki.org community is very active and supportive

In particular I think it is worth getting to know the skins and plugin structure to (i) make it look better and (ii) add your own goodies.

There is no benefit in using a relational database as a back end for a collaboration site like this - the things you want such as version differencing and free text search work well and fast using grep on flat files at this scale.

Is collaboration just a subset of content management... not in my humble opinion. TWiki is well balanced in its light touch (but available) security, user registration, locks and versioning - in my experience it is very hard to get users to actively collaborate and most content management systems employ a highly structured and therefore offputting UI.

PS. Not to mention T.120/NetMeeting style application sharing as collaboration.