Linux only: The Jaunty Jackalope release celebration continues. App Runner adds items to the Gnome context menu to launch executables or scripts directly from the GUI—even letting you easily run as root.
If you've ever come across instructions for using an installer or script that require you to drop to the terminal prompt and type in a command, App Runner would come in handy—just right-click on the file and choose Scripts -> Run this App instead. Most Linux readers will be quick to point out that the majority of software can be installed with a quick apt-get command—but there's plenty of scripts and closed-source apps that this would be useful for.
App Runner is a free download, requires Linux with Gnome.