Rofi is a window switcher, application launcher and dmenu replacement.

Rofi, like dmenu, will provide the user with a textual list of options where
one or more can be selected. This can either be running an application,
selecting a window, or options provided by an external script.

Rofi started as a clone of simpleswitcher, written by Sean Pringle - a popup
window switcher roughly based on superswitcher. Simpleswitcher laid the
foundations, and therefore Sean Pringle deserves most of the credit for this
tool. Rofi (renamed, as it lost the simple property) has been extended with
extra features, like an application launcher and ssh-launcher, and can act as
a drop-in dmenu replacement, making it a very versatile tool.