Do you like murdering thousands of little mans?
Do like makin waaagh like all good n' proper orks do?
Do you like engineering and tinkering with physics?Then buy Besiege from Steam for $6.99 USD you dolt.
Besiege is still under development (yes, yet another indie Early Access game), but right now is amazingly polished and a fun toy even as it is. Like many 'creator' style games, you're given a 3D environment, some blocks (from basic wooden beams, to flamethrowers, to hinges and springs, to wings, etc), and left to go play with them. The singleplayer mode gives some goals, usually in the form of a little puzzle each level often revolving around killing some little dudes, but the sandbox is available for those that just want to make cool machines.
And oh, what cool machines can be made.https://www.youtube.com/watch?v=w39KuV51Uho
Now go forth and murder mans. And remember, losing is fun!