"Move, resize & reorganize windows: make the most of your screen space." Window tiling for OS X.

"SizeUp allows you to quickly position a window to fill exactly half the screen (splitscreen), a quarter of the screen (quadrant), full screen, or centered via the menu bar or configurable system-wide shortcuts (hotkeys). Similar to "tiled windows" functionality available on other operating systems."

Fiddly, to say the least.

"With MercuryMover, you can move and resize windows on your Mac from the keyboard, positioning them precisely where you want." Not sure I'll spend a tenner on it, but it's pretty cool.

This would seem to be a bloody remarkable application. The facility for text searching images is particularly cool (business cards/wine labels/handwritten notes snapped with a webcam all worked well for me). At last, computers can fix my fried memory!

Looks lovely. No Linux version as far as I can tell, though.

Open source equivalent of Parallels or Fusion - still beta, but looks to be usable.

PC emulator for Mac

Not a PearPC rip-off, developer says, even though the version doing the rounds just now has PearPC code in it.