WebRetro (RetroArch)

Webretro is an emulator so you need a rom to use it. Some roms are at https://github.com/AlexBlackmore/roms but I suggest the GBA games because they're the coolest. WARNING: the save feature only works if you use the save feature in game (or if you're playing a game like sonic just get to a point where it saves then click save in the emulator)!