The Atari 800 emulator for GP32 and GP2x by Foft has been updated. Thanks to GP32x for the news. Changes:

Merged GP2X and GP32 versions (mostly)

Added ZIP file support

GP2X:Added clock speed change (Fast forward uses 250, let me know if it crashes for you)

GP2X:Fixed crash when displaying onscreen keyboard

GP2X:config now go in /mnt/sd/roms/a800 (i.e. move it from gpmm/a800 to roms/a800)

GP2X:Switched to 8-bit mode

GP2X:Added X and Y buttons

GP2X:Stereo works (thanks to Rlyeh again)

http://www.scrameta.net/a800.html