genorphan for gentoo
What is it: genorphan is a tools like debian's deborphan
It shows packages that have no packages depending on them.
The default operation is to search only within the libs
Tool aimed to hunt down unused libraries and packages
Dependnencies: epkg
SourceForge download page
Check, may be you already can use emerge to do it :)
Usage
Options:
-a search in all packages, not only in libs
-h or --help help screen
have a nice day :)