Don't get me started...

BIMserver presents itself as an open source BIM platform. What it does? It lets you collect files in IFC-format and put them in a central IFC-file.
You can issue a combined IFC-file from here, do revisions (and annotate them), use it for version control and do a clash detection based on rules set created in Java.

I'm no big fan of this piece of software:
There are better Clash Detection and more easy to use software solutions on the market, using IFC (Solibri) or native formats (Navisworks and Vico). You can write rules to use but you need a degree in Java programming to do that.
It isn't free. The software is free but has a really really long learning curve. Want ro learn it faster? A 2 day course costs a mere E8.000,-
It isn't new: look at the first line, there are other and better software solutions available.
IFC doesn't work properly. You loose a lot of data. To be fair: Revit particularly stinks at IFC, but even Archicad, which is supposed to have a good IFC export, looses a lot of intelligence.
Yes you can export IFC's from BIMserver back to the original software. These exports are a total disaster. ALL intelligent behaviour is gone. What's worse, these exports don't even recognise the same window types, CW's don't exist anymore, etc, etc. It's like trying to import a 3d dwg created in autocad 2000.
Development is slow. Maybe a logical result of it being open source freeware, but it looks like a major obstacle for me. Development starts and stops with the availability of funding and human resources.
It's IFC-based. Although a noble objective (complete open source bim-format), it's built for disaster. The development of IFC is also based on the willingness of a whole lot of participants, each with their own agenda. IFC has been under development for about 20 years or so, and it was surpassed in intelligence in Revit 5 (probably sooner, but I wouldn't know, never used those versions)

So, to summarize: commendable try, but no thanks...