VICE - Bring loops to life with the loop slicer plugin for Mac and Windows.
jGameBase - jGameBase is a fully-featured retro-gaming emulator frontend and game database utility.
GameBase - bu22.com - the home of the GameBase frontend and databases.
Z26 - Z26 is one of the best emulators for the Atari 2600.
Power64 - Power64 - Commodore64 Emulator for the Power Macintosh.
Javatari - Javatari is a multiplayer Atari 2600 emulator written in pure Java with no external libs.