The Ice Emulator is a homebrew project to allow gamers to be able to play emulated console games through Steam to take advantage of Steam's Big Picture mode. The game's GitHub repository has files, details, legal details, and more, including instructions on what emulators are required and how ROM support works. Currently this supports NES, SNES, N64. GameCube, PS1, PS2, Genesis, Gameboy, and GBA, and they are working on support for Wii, Dreamcast, and DS. Thanks Ant via reddit.