Some desktop environments have their own hotkey launcher
utilitity. This is nice, but also has a serious problem: if you
change the environment, you have to reconfigure all the hotkeys
(disgusting!). It's better to have a utility that do this task
separately.
The purpose of Xhotkeys is to provide this simple and easy
configurable hotkey launcher for the X-Window environment. It should
work on all desktops (Gnome, KDE, Xfce, ...) while you can still use
their own launchers. Xhotkeys has a graphical GTK configurator, although it's possible to manage the configuration file manually.
The source-code tarball and packages for Debian (so, Ubuntu also) are available.