CHeriCoS

The fine Open Source Collection Management Software known as OpenCollection until now has renamed to CollectiveAccess. As they say the renaming was caused by a dispute with a former project partner:

However, a former institutional project partner believes that the name "OpenCollection" itself (and only the name - not the software) is not free. They believe that they have some ownership interest in the name which competes with the Project’s ownership interest. After some consideration we have concluded that, while we clearly own the name, we would prefer to put our energy into continuing development of useful software tools for the community rather than waste resources debating the status of a label.

Collective Access is an Open Source Software based on PHP/mySQL and is developed by a company called whirl-i-gig. It's the only Collection Management System available open source that fits professional needs (as far as I now). It is very easy to install and to administer, but there is also professional (paid) support if you need one.