BetterTouchTool
Em Preferências → Configurações Básicas, selecione Janela Snapping. Funciona exatamente como no Windows.
BetterSnapTool
BetterSnapTool allows you to easily manage your window positions and sizes by either dragging them to one of your screens corners or to the top, left or right side of your screen. This lets you easily maximize your windows, position them side by side or even resize them to quarters of the screen.