MAME - mame_license.txt
DosBox - GPL.txt
openMSX - GPL.txt
Gens/GS - GPL.txt
NSFPlay - [Google Code lists Apache License 2.0]
Ootake - ?
in_vgm - ?
MEKA - ?
zlib - see zlib.h
in_wsr - ?
vbjin/mednafen - GNU GPLv2