Growl is a great utility for last mile notifications, but comes with terrible network support. It seems the most useful notifications are the ones coming from out there, not from your computer (do I really need to see the currently playing song from iTunes?). Unfortunately, Growl's network interface is based on some esoteric protocol and requires a direct connection.Yapper solves this problem and makes Growl instantly accessible from any system that can send Jabber/XMPP messages. Yapper runs in the background locally, like Growl, but listens on a Jabber account you specify. When messages come in, they get pushed to Growl. It's that simple.