As with most game consoles, there were many more games in development for the 7800 than were actually released. However, very few prototypes have been located, due to Tramiel Atari’s reluctance to make them in the first place. Atari 7800 prototypes tend to be highly coveted by collectors, often fetching hundreds of dollars when sold. Some collectors are unwilling to share the rare items publicly as doing so risks decreasing the value of their prototypes.
Nonetheless, some unreleased Atari 7800 games, as well as early versions of released games have been released to the public. A few have been manufactured and sold.
Klax (Programmed by Blue Sky Software). The game was nearly completed when canceled. For years, it was traded privately until a ROM was made available to the general public. Later, the developer appeared to create additional levels for the community.
Gato (Programmed by Ibid Inc Software). Released on the XE Game System, an Atari 7800 version was started but not completed beyond a simple demo.
Missing in Action (Programmed by Sculptured Software for TNT Games). A side scrolling adventure that was about 85% complete when cancelled. The game is mostly playable with some later collision detection issues requiring cheats to get past.
Pit-Fighter (Programmed by Imagitec Design). An early demo of the game has been found, with crude graphics, no sound and poor collision detection.
Rescue on Fractalus! (Programmed by GCC). A conversion of the popular computer game was released by GCC in 2004. The game was partially complete with a running engine but no enemies.
Other 7800 games remain lost, despite indications that development occurred. The most notable of these are Skyfox (shown on the back of the original system box) and Electrocop (artwork has since been uncovered).
Engineering Notes list Tempest as a game that was between 15–20% completed for the Atari 7800; no code to date has been found. The Atari Museum located and posted unreleased box art and notes for a 7800 version of Crystal Castles. No code to date has been found for that game either. Atari's earlier 7800 games listing showed Millipede as one of the games in the line up; however, it does not appear that it was ever started or worked on.