Okay, so here's something I never expected to add to the news... those with long memories might remember the April Fools video on the interwebs where one of the developers of Duke Nukem Forever claimed to have a working 2600 cartridge version of the game, developer Ed Fries has taken things one step further with Halo 2600. And yes, it really is a functioning 2600 game! The link below will take you to a Java-based emulator but the news source is a thread at Atari Age where the ROM is available to download and Fries himself gives a little more insight into the project.
• External link: Halo 2600 official page
• News source: Atari Age forum post