Nescube is an excellent emulator that allows you to play old NES games on your phone for free.
If you're a big Nintendo fan then Nescube is one phone app that you can't afford to be without. It works by loading ROMs, which are games files in .nes format containing all the data of the original game. You can download these files or use existing ROMs that you own. The compiled Nescube emulator comes with one preloaded game called Bonk's Adventures.
If you click on the 'Open game' option from the main menu and select 'Internet' you'll be presented with an A-Z list of games you can download and run directly in Nescube, ranging from Addams Family, through Super Mario Bros, to Zippy Race. Remember though, that downloading ROMs of games that you don't own is technically illegal, so consider yourself warned.
In terms of the games themselves, the reproduction of them in Nescube is totally faithful to the original game, with exactly the same graphics and sounds. Depending on the kind of phone you have, you may experience slow loading of games, distorted or jerky gameplay.
Luckily, Nescube comes with plenty of settings you can tweak to improve your gaming experience. For instance, you can tinker with display settings, adjust the FPS level and video rendering, and adjust the sound source and settings. You can also map keys on your device to controls to customize your playing.
If you were a Nintendo nut in your youth, then Nescube will send those childhood console memories flooding back.