The AEC Hackathon 1.1 starts today/tomorrow and they made a special category for open source BIM tools. For that reason we had a close look to our current codebase and decided to build a new release candidate. This is the latest of the latest (it is still warm), but obviously not very well tested…. Find it on our github page. Best of luck to all the hackers! And thank you AEC Hackathon for this great initiative!
Update: have a look at this wiki page for a short introduction of some popular open source BIM tools.