sdidentd (simple darwin ident daemon) is an ident deamon (rfc 1413) for darwin/Mac OS X. For trusted networks this daemon can still come in handy. This is a very simple implementation, and will return the real username when asked (and currently can’t be configured to lie). Unlike other implementations I found for mac, this daemon really checks the socket owner, and not just the currently logged in user.
sdidentd is available as open source at: http://code.google.com/p/sdidentd/.