Gridlee is a 1983 arcade game that was never officially released, but the code was later released for free for non-commercial usage in 2001. The App Store app uses MAME 0.139u1 (MAME4iOS) to provide the emulation engine for the game. MAME is a popular arcade machine emulator that will run thousands of arcade games if you have the original ROMs.
When launching the free app, users are greeted with the Gridlee game. TouchArcade readers, however, quickly noticed that additional ROMs could be copied into the App's ROM directory (without jailbreaking), revealing the fully functional MAME emulator.
When word of this hit our forums, readers were quick to pull out iExplore and begin digging about the app's directory structure looking for a ROM folder. Well, it's in there, and sure enough, if one copies other MAME ROMs into that folder, the Gridlee app starts up with the standard MAME4iOS ROM listing, allowing for a great many games beyond just Gridlee to be played on the iPhone or iPad in this Universal app.
The story is similar to the iMAME Emulator that was released into the App Store in December, 2011. Apple quickly pulled that app a few days after its release. While a number of individual emulators do exist on the App Store, Apple has been more restrictive about these open emulators, presumably due to potential legal issues.
Gridlee is a free download on the App Store. [Direct Link]