Licensing
Textpattern is free, open source software, distributed under the GNU General Public License as stated in Textpattern official FAQs. Therefor also all Textpattern plugins should use GPL compatible license.
Shortly said, rah-prefixed plugins share memory space, functions and data structures with Textpattern, and therefor rah-plugins will always use GPL v2 for the source code that is most likely written in PHP.