Play your PSP games in HD!
PPSSPP can run your PSP games on your PC in full HD resolution, and play them on Android too. It can even upscale textures that would otherwise be too blurry as they were made for the small screen of the original PSP. Even on modern Android phones and tablets, you can often run at double the original resolution.
February 1, 2015: 1.0! Finally, 1.0 is out, with a ton of new improvements! Note that it can take a while for it to become available in the Play store, depending on your location and Google's datacenters.