The open source BIMserver software is GPL v3 licensed. You can read the full license at http://www.gnu.org/licenses/gpl-3.0.html.
The BIMserver software also uses the IFC Engine DLL from TNO. This is NOT open source and not official part of the project. The IFC Engine DLL has its own license.
For questions about the license please send an e-mail to license@bimserver.org