z26 (an Atari 2600 emulator)

Z26 is one of the best emulators for the Atari 2600.
The author reports that the graphics part of the emulator
is nearing perfection to a point that there's little more
to fix.

Note to 64-bit users: z26 is mostly written in 32-bit x86 assembly,
so it can't be built for x86_64. However, if you build a z26 package
on a 32-bit system, and install it on a 64-bit system that also has
alienBOB's or Fred Emmott's 32-bit compatibility packages (specifically,
a 32-bit sdl package is required), it should run just fine.