ModuleManager is licensed under a modified CC share-alike license, under the terms spelled out by the original author, ialdabaoth, in this post:
http://forum.kerbalspaceprogram.com/threads/31342-0-20-ModuleManager-1-3-for-all-your-stock-modding-needs?p=528607&viewfull=1#post528607

The version of ModuleManager included with this (2.x.x+) has been maintained and expanded by sarbian, and is not the original ModuleManager created by ialdabaoth.

More information can be found here: http://forum.kerbalspaceprogram.com/threads/55219