Emulators: ... and the rest
This section primarily deals with platforms where no highly usable homebrew emulator exists, or platforms that are considered very niche.
[Atari 2600] Activision Anthology
This is a commercial Atari 2600 emulator that's packaged with the games released under the Activision brand, along with some prototypes and homebrews Activision was given permission to include. Imagic games, which are also owned by Activision, are not included. Apparently, this emulator is coded by Bradford Mott, the author of Stella (a multi-platform 2600 emulator). Since it's coded in pure C++, and may well be a port of Stella, it runs slowly. Furthermore, the games were hacked to run faster, which makes it harder to inject other games (though this may be possible), yet still the emulation isn't full speed. However, it is the only working 2600 emulator out there.
[Atari 2600] 2600_vcs
This partially finished 2600 emulator was abandoned in 2001. Apparently, the author was having problems with speed (1 FPS), but source code is available for interested parties.
[Atari 2600] Gameboy Advance Atari 2600 Emulator
This creatively named and abandoned 2600 emulator was written by TwoHeaded software. There are shots of Pitfall running on the real hardware on the website. It was written in C++, which may have been its downfall. Interestingly, the files below reveal a lot more information about the emulator. It appears that this was going to be the Activision Anthology, but perhaps the lack of speed led to the project being handed to Mr. Mott instead.
[Atari 2600] GBAVCS
This unreleased emulator was written in assembler, but never fully worked on real hardware. Unfortunately, the website hasn't been updated since June 2001, and the author, Otaku, is bound by a non-disclosure agreement and cannot release the emulator itself.
[C64] Splam
Although we got ZX Advance, many were hankering for that other 8-bit computer giant, the C64, to make an apperance on the GBA. It looked so promising for a long time—a SID player was released (SPLAM!SID), and an emulator called SPLAM was announced. And then: nothing. The SPLAM website has long since vanished, and it appears the project is dead. Check out the screen grabs below (originally on www.gamershell.com) for a look at what might have been.
[Lynx] GBA Atari Lynx Emulator
This is the only GBA Lynx project known, and it hasn't been updated since 2002. The emulation is currently up to 10 FPS, and the emulator was due to be re-coded in ASM from C++. The graphics engine still needs to be re-coded, along with some of the CPU core. There is currently no sound engine, and this may or may not be a possibility in the future.
[Sharp X-1] X Millenium Advance
This is a Sharp X-1 emulator that plays a variety of games. We're unsure what the features are, as the readme cannot be translated by Babelfish, but the file includes its own compiler. If anyone can shed some light on the features of this emulator, please contact us.