I think I paid $1.99 for this 5 or so years ago. Hands down the best $1.99 I've ever spent.
Seconded. I use + love BetterSnapTool. Works great.
Best tool ever. The custom touchpad gestures are great, too. You can do stuff like three-finger swipe up/down to switch to previous/next tab, and rotate right/left to open/close taps.
I hardly ever use the touch gestures but BTT will let you drive everything from the keyboard. I can put windows almost anywhere at will now.
I know I'm being selfish here but it would be nice if Apple covered this sort of stuff instead of concentrating on emoji and Siri. Both of which I have no real use for.