Drastic is an amazing emulator for Android do Nintendo DS. There are other Nintendo handheld emulators for Android, but DraStic stands out for its emulation speed, even on intermediate or old devices such as Galaxy S2.
http://www.youtube.com/watch?v=idx3_ydw6e4As possible in the video above, the emulation is extremely decent. With minimal framerate drops and perfectly playable, including with the audio.
Of course not all games are compatible, but just for emulating Mario Kart do DS e New Super Mario Bros, DraStic already deserves its R$ 18 reais.
Yes, the emulator is paid, but you can try the demo version to test the emulation on your smartphone or tablet. It's a good idea before purchasing the paid version. The free demo version has a 20 minute gameplay limit.

Note Not compatible with smartphones and tablets with Tegra 2 or x86 processor (Intel, such as Razr i)
Link to Download on Android (Paid)
Link to Download the Free Version (Demo)
Advertising: No | Internet connection required: No
Contains built-in purchases: No
In English
Requires Android 2.2, 2.3, 4.0, 4.1 or Higher
[originally published August 20, 2013]