… whether the guys behind this (http://code.google.com/p/giver/) know about this (http://techn.ocracy.org/telekinesis/)?

It’s a pleasure to see as many projects as possible making use of Avahi (http://avahi.org). OTOH I believe that all solutions should speak the same protocol. Using Apple’s somewhat standardized link-local iChat/XMPP protocol (which is what Telekinesis does) seems to be the best option to me: because you get MacOSX interoperability for free and many IM clients (including many on Windows) already contain support for this as well.