debbugs

?JossMouette: Another example that comes to mind is the BTS usertags. Although there is no convenient interface to browse them, they are already used for many applications, my favorite being bts-link-upstream - another tool we've started using the day it was implemented.

CIA

?JossMouette: I should also mention CIA, which dumps all SVN commits on #debian-boot and #gnome-debian. This is extremely useful to follow what's going on without flooding a mailing list that's hard to read.

reportbug

Steinar: "Changes in reportbug quickly reflect in bug reports"