Atari 2600 emulation is available for most major operating systems and is now very accurate. Despite the relative simplicity of the 2600 system, it is not an easy system to emulate. While it does not require a lot of computational power to emulate the 2600, it is hard to accurately do so. For example, because of the lack of a frame buffer, 2600 emulators must not only emulate the console, but the television as well. Due to the longevity of the system, many 2600 games used undocumented features, and even exploited bugs in the hardware to squeeze the most out of the system, doing things even the original designers would deem impossible (a notable example is the starfield of the game Cosmic Ark). It took some time for the emulator programmers to mature their software to properly emulate the undocumented features, bugs and quirks of the system.
The MESS emulator supports recording and playing back of Atari 2600 emulation sessions. The Home Action Replay Page (aka HARP) allows Atari 2600 users to archive their favorite play sessions of the Atari 2600 system and its games.
Some well known Atari 2600 emulators today are:
Stella - An open source, multiplatform emulator (Windows, Mac OS X, Linux, Dreamcast, Nintendo DS, Wii, GP2X).
z26 – Another open source, multiplatform customizable emulator (Windows, MS-DOS, Linux)
PC Atari Emulator – Easy to use, very fast emulator (Windows, MS-DOS). Handles the Cosmic Ark starfield effect correctly.
MESS – the multi system emulator that supports all old Atari console systems
The Pocket VCS – PPC – Easy to use, very fast and emulator (Windows Mobile).
GP2X-2600 – An emulator for the GP2X handheld console