the FSFE has started a campaign on http://pdfreaders.org/
I suggest adding GNU GV to the list -- http://www.gnu.org/software/gv. Like others already on the list, it is a Ghostscript front end. (Why be coy and say "other software"?) I was surprised to see another package named "Yap". The Yap I knew has been the DVI viewer for Windows included in the MiKTeX distribution for many years. http://en.wikipedia.org/wiki/YAP mentions both. Anyway.
