My student Charlie Curtsinger pointed out a better alternative to Cinch: BetterTouchTool. The name is not as nice, but unlike Cinch, BetterTouchTool lets you snap windows to corners. By default, these occupy 1/4th of the screen, but the proportions are adjustable. I have only been using it for ten minutes, but it works great – and Charlie says he has been using it for a while without any issues.