Debian is one of the oldest and most well-known Linux distributions.
It is created and distributed entirely by volunteers, which explains some of its characteristics: the quality is very high, but the flashiness factor is often low. It is very easy to keep the system up to date, and there are thousands of packages available. Of particular interest to Tcl'ers, Debian has versions of Tcl, Tk, tcllib, BLT, expect, snack, Rivet, AOLserver, tkcon, itcl, tix, xotcl, tclvfs, Img and a host of other packages.
David Welton is a Debian developer.
More information is available at http://www.debian.org
Other distributions used and recommended by Tcl'ers: Suse