A surprising number of GNU/Linux tools have animal names (rather than simply having animal mascots or logos).

First, obviously, there's :gnu, and also...
:dolphin-emu (two for one)
:firefox (apparently a red panda)
:pidgin (close enough)

Non-free, not on GNU/Linux or I don't use them:
dolphin (KDE file manager)
gecko (browser engine for firefox/icecat/iceweasel)
icecat / iceweasel

Close contenders:
:munin (famous raven)
:ubuntu (release names)

Distant contenders:
:gencfsm (sounds like a sneeze)

See also | Meet the free software gang

CC0 / Public domain dedication To the extent possible under law, d3vid seaward has waived all copyright and related or neighboring rights to "Menagerie in Grasmere notebook, including code snippets" (why? how?)