Mac OS X only: Open-source donationware application Afloat adds several useful tools and effects to your windows. We've mentioned Afloat once before, but it's since updated with a more polished look and tons of new features. Apart from standards windows effects like transparency and always-on-top floating, Afloat can reveal the file a window is displaying through a shortcut (Cmd-Ctrl-Up) or keep a window on top as you switch Spaces on a per-window basis. The new and improved Afloat is part eye candy, part productivity, but unfortunately it only works with Cocoa-based apps like Safari and TextEdit, which means popular apps like Firefox and even iTunes are left out in the cold. Afloat is donationware, Mac OS X only.