PCAE?

The PC Atari Emulator, or PCAE, is an MS-DOS program designed  to
emulate  the  famous  Atari 2600 Video Computer  System  on  PC's
compatible  with  the Intel 80486 CPU or better. It  accomplishes
this with an emulation engine that is written almost entirely  in
assembly language, with extra features written in Borland  Pascal
7.0 for DOS.