GNU Linux .. What kind of an idea came to your mind? Its free and open for everyone to use. But I recommend to use community supported Linux OS ! So nowadays most popular Linux Distributions are
Ubuntu is the most popular Linux distro available in the society these days.Ubuntu supports .deb packages to install and when you want to install a new software it should contain .deb extension.
Ex – google-chrome-stable_current_i386.deb which is the Google Chrome Package for Ubuntu which supports x86 architectures(32bit).
Debian is same as the Ubuntu OS and the architecture,package management is same as Ubuntu.So latest version of Debian is 6.0(Squeeze) available in debian.org.
Fedora is same as Redhat Linux but Fedora is community supported OS.Main Difference of Fedora with compared to Ubuntu/Debian is Fedora use rpm package management(Redhat Package Management) and pacages available in .rpm extension
Ex – jdk-7u1-linux-i586.rpm which is the java package available for fedora x86 OS architecture.