This is Counter-Strike 1.6 running just fine on a mobile telephone. Servers and everything.
Is it the ideal way to play the game? No. But it’s a lot more practical than folks trying to get Doom running on calculators and ATMs.
The touch controls look like a pain, but this being Android, it’s not going to be hard hooking proper peripherals up to your tablet/phone if you need more precision.
If you want to try it out, you’ll need 1.6 in your Steam account for some of the necessary files. For everything else (including instructions), head here.