bsnes Licensing Agreement:

You are free to redistribute this software, and its source code; provided
there is no charge for the software, nor any charge for the medium used to
distribute the software. You are also free to use and modify the source code
as you desire for personal use only. No publically-released derivative works
of this source code are permitted without my permission. You must also abide
by the terms of any additional source code licenses contained within my code.
At present, this only includes the mode7 renderer, which was derived from the
snes9x mode7 renderer.