If you want to check if all the packages you have installed on your Linux (Debian based) are free software you can use the vrms software to check it.

vrms is according to its site:

The vrms program will analyze the set of currently-installed packages on a Debian-based system, and report all of the packages from the non-free tree which are currently installed.

Installing and using it

sudo apt-get install vrms

vrms

The output on my PC was:

fglrx-control             Control panel for the ATI graphics accelerators
fglrx-driver              Video driver for the ATI graphics accelerators
fglrx-driver-dev          Video driver for the ATI graphics accelerators (devel
fglrx-kernel-2.6.18-3-686 ATI binary kernel module for Linux 2.6.18-3-686
fglrx-kernel-src          Kernel module source for the ATI graphics accelerators
fglrx-sources             Source code for the ATI graphics accelerators control
opera                     The Opera Web Browser
skype                     Skype - Take a deep breath

  8 non-free packages, 0.7% of 1127 installed packages.