Perl bindings for the C library "libunique" that provides a mechanism for
writing single instance applications. If you launch a single instance
application twice, the second instance will either just quit or will send a
message to the running instance.

Unique makes it easy to write this kind of applications, by providing a base
class, taking care of all the IPC machinery needed to send messages to a running
instance, and also handling the startup notification side.

WWW: http://search.cpan.org/dist/Gtk2-Unique/