openDCIM is a free and open source solution for DataCenter Infrastructure Management. It is already used by a few organizations, and is quickly improving due to the efforts of its developers.
I have written a complete, bottom-up installation for openDCIM on CentOS. This will get you up to the first screen in the web interface, after which you can follow Scott Milliken's video tutorial for the initial settings of the application.
The guide is written for openDCIM 2.1, but should be fairly applicable to newer versions.