Here is a list of options for user-programmable Atari 2600 cartridges.
Harmony Cart: http://harmony.atariage.com/
Melody Cart: http://www.atariage.com/forums/blog/107 … t-harmony/
DIY EPROM / EEPROM Cart: http://www.atariage.com/2600/faq/index. … 00#pinouts
AtariAge / PixelsPast EPROM Cart PCBs: http://www.atariage.com/features/shows/ … spast.html
Krokodile Cart: http://www.atariage.com/software_page.h … belID=2716
Cuttle Cart: http://www.schells.com/cuttlecart.shtml
Modified SuperCharger: http://www.biglist.com/lists/stella/arc … 00022.html
Modified VecFlash Cart: http://little-scale.blogspot.com.au/200 … -2600.html
Am I missing anything?