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.