This is a freeware graphical RCon tool made with Qt. Although you can use it with any Quake 3 distribution, it was mainly developed for ioUrban Terror.
Freeware for Windows, Linux and Mac OS X
Screenshot
Downloads
QRConUtil 1.0 beta for Windows
QRConUtil 1.0 beta for Mac OS X
Notes
* Note for the Linux version: you will need to install Qt 4.7 in order to run the program! If you’re using Ubuntu, you can install it with the following command: sudo apt-get install libqtcore4 libqtgui4 libqt4-network