This tool is a simple "run-program" window, something like "xrun" or "gnome-run". However, those other tools don't have some nice and important features: the very useful feature that allows one to use it with keyboard only, and to be fast enough. If you saw KDE, it's window manager (KWM) provides a key combination (ALT-F2) that opens such a window. The features there are pretty nice, such as it supports URLs, completion from history, TAB completion for files on the local filesystem, etc. Because GNOME didn't had such thing, here it is: gmrun, that provides pretty much the same behavior as the KDE's ALT-F2, only it's more configurable.
WWW: http://gmrun.sourceforge.net/
None