This awesome id3-tagging program was available for 5.04 but wasn't transferred to 5.10 - only the "normal" and old "cantus" package is available. Would be nice if someone redid it for 5.10. :)
Cantus3
Archived thread 75172 from Deferred/Invalid Requests. Markdown source: DeferredInvalid_Requests/thread_75172_Cantus3.md
I'm guessing it's missing from universe in breezy because it got orphaned in debian. So the correct solution would be to find a debian maintainer for the package.
Upstream mess -- I guess I'll defer for now.