2x0ng (and its predecessor, Xong) is a hybrid roguelikes that has the appearance, sound and mechanics of Atari age games. Levels are randomly generated, and the rules are up to you to discover. Here is a video review for your elucidation. Available for PC, Mac and Linux.
Atari Confidential Design Documents Now you too can read the hardware specification for Gauntlet. Add a C compiler or assembler and a dash of MAME and you can write your own game.