This is Clash of Stone, a supplement for the d20 epic game that takes it from the Middle Ages to the Stone Age.
You will have a base, a castle, from which you can fire the catapults it has by using the mouse or your finger to set the angle and then letting go to fire. Skeletal enemies put in different places are your targets. They want to destroy your castle.
Either you kill all the skeletons and their catapults first in a level, or they destroy your base first, which means you lose. It gets harder with each level, but it's also a lot more fun.
Have fun and good luck!
