The application is in the Ubuntu repositories, so you can easily install it using Synaptic, but a newer version just came out which fixing some bugs which you can download from here.
For installing it in other Linux distributions, see FSlint homepage (there are packages available for Debian, Fedora, RedHat, openSUSE, Gentoo and Mandriva).
To run it, press ALT + F2 and type:
fslint-gui
[via Ubuntu tips]