Clockwork is licensed under the GNU General Public License, the most loved and hated of Free Software licenses.
Peruse it at your leisure here.
The short of it is that you are free to use Clockwork in any environment, be it personal, commercial, governmental or not-for-profit. You are guaranteed access to the original source code, and your ability to modify, hack it, and rework it is protected.
Just keep in mind that if you redistribute—with or without modification—you have to give those same rights and protections to the next guy. We (the development team) do ask that any changes, bug fixes or enhancements be sent back to the community so that we can all benefit.
More about this hippie code-sharing mumbo jumbo can be found on the Why Clockwork is Free page.
The Clockwork website is licensed under the Creative Commons Attribution-NoDerivs 3.0 United States License