I wanted to work more on the actual project before writing about it, but I’m lazy, and dear community may be not.
At Wikimedia we have one database server which replicates from multiple (like 15!) masters. It even splits replication streams by database, and applying changes in parallel.
All this stuff is done by external replication agent, Trainwreck. It is public-domain software, which was written by River, doesn’t have much documentation, works only on Solaris (River likes Solaris), unless you comment out all process management blocks, which use doors and other Solaris specific API.
It lives in Wikimedia SVN, and can be checked out using:
svn co http://svn.wikimedia.org/svnroot/mediawiki/trunk/tools/trainwreck/
It sits there, maintained just for needs of that specific single server (ok, there might be two or three), so if anyone wants to make it available for broader audience, feel free to fork a project to some community-oriented place, add all nice features you need. :)