Source: http://8bit-unity.com/

The project of a guy named 8-Bit Dude sounds like a SCAM at first sight. 

Quote: You have some great ideas for a game on 8bit era computers, such as the Apple //e, Atari XL/XE, Commodore C64, Oric 1/Atmos or Atari Lynx... But you don't have any clue about assembly language programming? 8bit-Unity is the only cross-platform C language SDK for 8bit computers, which allows writing your game just once, and then deploy it on all those platforms!

What sounds so tempting is still in the beta stage, but is already quite mature and usable. 

8-Bit Unity is currently available in version 0.4.0 and really allows builds for Apple //e, Atari XL/XE, Commodore C64, Oric 1/Atmos and Atari Lynx. The integrated asset pipeline makes life much easier, because only one master asset needs to be produced for bitmaps, sprites and music, which can then be easily adapted to the corresponding target systems.

As a one-man-show-project it is really impressive. But to what extent you can produce complete titles with the SDK is not foreseeable from our side. But it should be worth a test in any case.