jg-prosystem (Atari 7800 emulation core for Jolly Good Emulation) ProSystem JG is an emulator for the Atari 7800. This is a fork of ProSystem 1.3e with patches from OpenEmu, which contains patches derived from Wii7800 and js7800. Note: Although the Atari 7800 can play Atari 2600 games, this emulator only supports 7800 games. Filenames supported: .a78 To run files with other extensions: jollygood -c prosystem By default, no controls are mapped. The first time you run a game, press Shift-1 to configure the first controller. Then press Shift-3 to map the controls on the console (Reset, Select, Pause, Left/Right Difficulty).