Debian is the most common and most stable linux distribution used for servers. It’s (said) stability also means packages can be rather outdated though, which you need to be aware of if you want to try or use newer software versions.
Lifecycle of packages through the different distribution repositories, and the release-names.
[experimental](http://wiki.debian.org/DebianExperimental) > [unstable](http://wiki.debian.org/DebianUnstable) > [testing](http://wiki.debian.org/DebianTesting) > [stable](http://wiki.debian.org/DebianStable) running development distribution “sid” next release 2007 4.0 “etch” (support until 2010) 2009 5.0 “lenny” (support until 2012) 2011 6.0 “squeeze” (support until TBA) 2012 7.0 “wheezy” (not released yet)
- Contrib: Free software depending on non-free software.
- Non-Free: Non-free software.