Those are:
1. Not precise name collisions.
2. All mail-notification utilities, as was the original biff.
And since we're mentioning Debian, it has a policy requiring unique names within the Debian archive to be unique. Precedence goes to the earlier software packaged. Installed programs must also have unique names within a given system. The datetime Swiss army knife utility discussed here violates both policies.
As Debian policy is used both for Debian and derived distros (see: <https://en.wikipedia.org/wiki/List_of_Linux_distributions#De...> for a partial listing), it has considerable influence.
I've renamed the project to bttf :-)
That works on Debian ;-)
<https://packages.debian.org/search?keywords=bttf>
Might want to ping the mods (hn@ycombinator.com) to update this submission title.
Edit: I'd typoed "bttf" as "btff" initially. Corrected shows partial but not exact matches on "libttfautohint1" and variants.