Be quick before its gone again. Gridlee was released today as an old unreleased arcade rom in the AppStore. You can use a program like iExplorer to add other games into the Roms folder just as you did with iMAME before it was pulled last year. It's universal and free but you will have to be quick.
http://toucharcade.com/2013/01/26/mame-is-back-in-the-app-store-for-now-with-gridlee/
http://toucharcade.com/2013/01/26/mame-is-back-in-the-app-store-for-now-with-gridlee/