KEGS is an Apple IIgs emulator for multiple platforms (Mac OS X, Windows, and Linux/Unix). Its acronym stands for Kent's Emulated GS.
It is capable of emulating a IIgs with 8-120 MHz, and runs most applications and games.
A Windows port, KEGS32, is maintained, as is KEGS-OSX, a Macintosh port. XGS-DOS, an MS-DOS port, was last updated in 1998.