zero configuration networking
works on OsX. some apps use it eg. ichat, subethaedit, shared-space, etc+.
There is an SDK for linux/bsd/windex http://www.swampwolf.com/products/ but few crossplatform gadets have appeared…
http://developer.apple.com/macosx/rendezvous/
avahi → linux/BSD
linux mag feature “Zeroconf Disassembled” http://www.linux-mag.com/cgi-bin/printer.pl?issue=2003-08&article=zeroconf