LaunchBox - LaunchBox is a portable, box-art-based games database and launcher for DOSBox, emulators, arcade cabinets, and PC Games. Download it free!
ScummVM - Game engine recreation of SCUMM made by LucasArts.
GameEx - GameEx is considered to be the most powerful and feature rich front-end for MAME, GameBase, Daphne, PC Games and all command line based game emulators, along with being a complete Home Theatre PC solution.
DOSBox - DOSBox is a DOS-emulator that uses the SDL-library.
GamersGate - Buy and download games instantly for PC and Mac.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.