LaunchBox - LaunchBox is a portable, box-art-based games database and launcher for DOSBox, emulators, arcade cabinets, and PC Games. Download it free!
Mitch - The unofficial mobile app for itch.io
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.
GameDatum.com - A platfrom of free online games. A list of all the available online free games from various producers online.
GamersGate - Buy and download games instantly for PC and Mac.
ScienceGameCenter - The goal of the Science Game Center is to demonstrate to teachers, scientists, museums, and parents the myriad ways games can be used to improve education in math and science.