KDE

I am pretty sure you know what the ALT-F2 does; viz. opening a "Run Command" dialog. What you did not know is that you can do a lot more than just enter program names and click on "Run".

Some interesting things you can do with it.

Calculator: 2 + 4
Send a Email: user@domain.com
Visit a website: http://www.hyperionreactor.net
Google: gg: Norrix
Google Images: ggi: Gorillaz
Dictionary: dict: Linux

MiniCLI makes this possible.