GetIt lets you can quickly install software, by using Windows Start Menu Search on Windows 7/Vista, or by picking them from a list on Windows XP.
GetIt is a front-end to multiple Application Getting engines that exist on Windows. All repositories are indexed locally, so you choose which program to install from a master list of all available programs. You choose the program you want to install, and GetIt knows which app-getter to talk to in order to make the installation happen.
GetIt is open-source software, licensed under the GPL.