The Atari 7800 ProSystem, or simply the Atari 7800, is a home video game console officially released by the Atari Corporation in 1986. It is almost fully backward-compatible with the Atari 2600, the first console to have backward compatibility without the use of additional modules. The 7800 has significantly improved graphics hardware over the 2600, but uses the same audio chip. It also shipped with a different model of joystick from the 2600-standard CX40.
You can browse and download most available games for free below, but you will need an emulator also to play them. For Atari 7800 we recommend http://emu7800.sourceforge.net/ but you can use any emulator of your choice and even original hardware if you have the know how!