Since February-2015 ThinkComposer is an open-source product, licensed under the GNU General Public License 3.0.
This roughly means that you can freely download, share, modify or extend it, as long you provide also a free copy of the original source code plus your own modifications and extensions.
The source code is available on CodePlex at: http://thinkcomposer.codeplex.com/
Conceptualize, model and visualize your Ideas! 