History: Tiki vs Bitweaver
Preview of version: 5
Bitweaver is a fork of TikiWiki. It was done in 2003 because some people thought TikiWiki was too bloated. BitWeaver's motto is 'Packages are King', and has frequently alternative ways to do the same thing (Search and ILike, or PigeonHole and Categories) while Tiki integrates all features in the same release.
Two major differences between the engines is that Bitweaver does not advertise any consultants, and does not (by default at least) starts with parallel tracks/webs/servers/ (main, docs, dev, etc.)
At time of writing (may 2010), Tiki5 is getting released, while BitWeaver 2.1 has been released in 2009.
Since I failed to install Tiki5 (database issues), I'll try Bitweaver and post more in this page ... I swear I'll (try to) stay objective.
Wiki Matrix
Compare them at http://www.wikimatrix.org/compare/Tiki-Wiki-CMS-Groupware+Bitweaver