Emulators are programs that run software written for old computers or videogame consoles on the new hardware. Essentially, an emulator makes old software "think" that it is running on the original hardware, while it actually runs on your computer.
The developer has been creating emulators since 1993 and has now moved onto mobile devices such as PDAs and cell phones to make them capable of emulating older hardware.
Due to its simplicity, ColEm has been integrated into and is now considered the daddy of all mobile emulators. If you want to be able to pl all your old mobile games, then give this a go.