Yamruby Copyright (C) 2013 Minao Yamamoto
Yamruby is free software distributed under the terms of the MIT license reproduced here. Yamruby may be used for any purpose, including commercial purposes, at absolutely no cost. No paperwork, no royalties, no GNU-like "copyleft" restrictions, either. Just download it and use it.
Yamruby is certified Open Source software. [osi certified] Its license is simple and liberal and is compatible with GPL. Yamruby is not in the public domain and Minao Yamamoto keeps its copyright.