Atari 5200 is a console made by Atari in 1982. The console did not take off due to the controller with its analog stick problems, Atari still focusing on the 2600 and the North American Video Game Crash affected any chance of success. By the end, only 70 games were commercially released for the console and it was not released outside of the US. There were more games unreleased and some have had their ROMs dumped.
While it is based off the Atari 8-bit computer range in terms of hardware, it is not compatible with it.
Done by the same developer as the VirtualDub software, Altirra is mainly a very accurate Atari 8-bit emulator but it does support 5200 games. The downsides are that it is not easy to set up and it is Windows only.
kat5200 is an easier emulator to set up and also supports some of the Atari 8-bit range as well. There are issues running some of library such as Bounty Bob Strikes Back not working and there are no sprite ripping features. Oh and make sure your ROMS are unzipped otherwise the emulator won't run them properly, you can tell a game is running properly when the game name appears on the Atari boot up screen.