ShiftIt is an application for OSX that allows you to quickly manipulate window position and size using keyboard shortcuts. It intends to become a full featured window organizer for OSX.
This is a sub-fork from the original [ShiftIt] by [Aravindkumar Rajendiran] which is not longer under development, and builds upon other people's work to add a few things I like, such as one-sixth incremental window sizing and a "large tile" that occupies the left 2/3 of the screen like in some tiling window managers.
Version 1.5.2 adds Undo support - you can now restore previous window positions (as long as they were handled by ShiftIt)
Please refer to the forks listing for more documentation and related work (kudos to the folk who picked this up before I did).