LaunchBox - LaunchBox is a portable, box-art-based games database and launcher for DOSBox, emulators, arcade cabinets, and PC Games. Download it free!

Playnite - Source code generated using layoutit.com

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.

Lutris - Lutris is an open source gaming platform for GNU/Linux.

GamersGate - Buy and download games instantly for PC and Mac.

RetroArch - RetroArch is a frontend for emulators, game engines and media players.