Techman there's a mobile version for Android and iOS if you can get it. It's updated often, and has many new mechanics, recently undergoing a huge update. Check out the Discord for it too if you can.
In case anyone is stuck on the Terminator T-14 Mission in the Alien Campaign, giving the Barret a 12x scope and sniping from afar when the robot is low is how you do it. You have to get all 5 kills to get 3 stars, and it's best if you make at least 2 bonuses on all kills.
Also if you're early on, the Punisher, Burster and Pulsator are the best weapons. The Pulsator is really good with Burst Shot and 12x Scope upgrades, at that point it is probably the best sniper, because it has more ammo than the Barret and Holy Grail, and fires faster. And if you don't mind about a bit less range, get the Carbon Stock upgrade for the Pulsator also, it adds a good bit of damage, and a some accuracy also.