The version you're referring to, 509494, is a specific build of the Dolphin Emulator for Android. The "MMJ" in the filename likely stands for "Mega Meow Japan" or a similar abbreviation, possibly indicating a customized or modified version of the emulator.
Dolphin Emulator is a free, open-source emulator that allows users to play games from Nintendo consoles, such as the GameCube and Wii, on their computers and mobile devices. The emulator is available for various platforms, including Windows, macOS, Linux, and Android.