Mac only: Open-source window manager Afloat updated to version 2.0 today, with complete support for Snow Leopard and a couple of new features, such as pinning to the desktop and resizing windows from anywhere using keyboard shortcuts.
We've talked about Afloat before, but ever since Snow Leopard's release, it and many other InputManager-based utilities no longer work, so early OS adopters have been left behind. Today, Infinite Labs updated Afloat to version 2.0, giving Snow Leopard all the features we've come to know and love, including window transparency, keeping windows on top, and turning windows into an unobtrusive overlay, where all clicks "fall through" the window onto the window below it.
Also notable is its ability to move a window from anywhere (not just the title bar), show a window's file location in the Finder, and keep a window on all of your spaces. Each of these optional features is just a keyboard shortcut away—though if you're not the shortcut type, they are also all available under the "Window" menu of the application in question.
The new version of Afloat doesn't just fix its Snow Leopard incompatibility, either—it includes some new features, like "pinning" applications to the desktop and resizing a window from anywhere (not just the corner). The only downside is that Afloat only works in Cocoa applications—which means that carbon apps such as Firefox and iTunes are out, sadly—but nowadays, most Mac applications are written in Cocoa, and thus should work with Afloat.
Afloat is a free download, Mac only.