Looking to kick it old school and play some Contra on your Android device? There's an emulator for that. Since the release of Android, emulator apps have come and gone -- some pulled by Google, some just simply no longer supported any more by their developers. However, if you're looking to replace some of those that have disappeared you can check out some of the ones available from Marat Fayzullin.
- iNES - iNES emulates classic NES and Famicom videogame consoles from Nintendo. It plays NES, Famicom, DiskSystem, and VS System games in a desktop window or full screen. Save game at any time and restart from that point later. You can also use GameGenie cheat codes, make screenshots and save game music in MIDI format.
- MasterGear - The MasterGear emulates several 8bit videogame consoles from SEGA. It plays Master System, GameGear, Mark 2, Mark 3, SG1000, SC3000, and SF7000 games in a desktop window or full screen. You can save game at any time and restart from that point if you get killed, make screenshots, and even save game music in MIDI format to play it later.
- VGB - VGB emulates Nintendo GameBoy handhelds and their accessories. It plays GameBoy, GameBoy Pocket, GameBoy Color, and Super GameBoy games in a window or full screen. VGB also supports the Pocket Printer, GameGenie cheat codes, and more. Please notice that VGB will not play GameBoy Advance games: you will need VGBA for that.
- VGBA - VGBA emulates the Nintendo GameBoy Advance handheld. It plays GameBoy Advance games in a desktop window or full screen. Please notice that VGBA will not play classic GameBoy games: you will need VGB for that.
Marat has quite a few others available for more obscure systems as well, if you're looking to check them out you can hit the source link for more details and download links to all listed.