Most of the apps that pass 50 million downloads on the Play Store are ones from major companies, but not this time. The newest app to join the 50 million club is PPSSPP, the popular open-source emulator for the Sony PlayStation Portable.
PPSSPP has been in active development for a few years, created by Henrik Rydgård (one of the co-founders of the GameCube/Wii emulator Dolphin). Like all console emulators, it took a while to get commercial games running, but compatibility is pretty good these days. Not only can PPSSPP play games at a higher resolution than the PSP's original 480x272 screen, but it also supports advanced features like texture scaling and anisotropic filtering.