Note that File::Which can also search for all matches too if you use it in a list context, e.g. @paths = which('foo'). File::Which also comes with a pwhich CLI utility which also accepts multiple arguments and has the -a switch to print all matches. The output format is slightly different than 'multiwhich' though.
In fact, the Unix 'which' command (or at least its Debian variant) also sports the -a switch.