Window managers are numerous on the Mac, with most relying on keyboard shortcuts or edge snapping. Moom is different.
Moom integrates into the existing Apple UI by providing a pop-up menu when you hover your mouse over the green "maximize" button in the top left-hand corner of your window. Clicking on one of the Moom menu options moves and zooms (mooms) your window to the desired sector of the screen. By default you've got horizontal and vertical half-screen configurations as well as full screen. If you want a quarter screen window, you can click and drag on the default Moom buttons to define the desired quarter.
Sending the window to another monitor is as easy as dragging one of the buttons in the desired direction of the monitor. A grid below the buttons allows you to quickly define a new size and position by selecting the squares required. If all your Mooming gets a bit crazy, you can move the window back to its original position with the revert arrow. You can also define custom mooms in the settings, which are then accessible via a drop-down menu from the Moom pop-up or menu bar.
Moom also includes robust support for keyboard shortcuts, including binding of window sizes and positions to individual shortcut keys. Moom takes keyboard usage one stage further with a keyboard control mode in which you can move the window around with the arrow keys, moom a window to any of the half-screen configurations, send it full screen or centered and even send it to the next monitor.
Moom is also able to run as a menu bar icon, a standard OS X program or even "faceless" (hidden).
We've covered a few other window management utilities on TUAW, but it's safe to say Moom is one of the best. For US$4.99 it's going to be one of the first apps I install on a Mac from here on in. If you're not convinced, give the free trial a go from the Many Tricks website.