> FBI Surveillance Van 2
I've heard of people doing this to scare the crap out of their low-key criminal neighbours.
> box1!box2!box3!userhandle
That's called Source Routing, and is what cjdns [1] does, although in a more federated and private manner. There's an OpenWRT firmware called meshbox [2] that works on the same devices as PirateBox (and more).
There's no apps shipped with it, but instead you get a secure, adhoc, near-zeroconf mesh network.
[1] https://github.com/cjdelisle/cjdns [2] https://github.com/SeattleMeshnet/meshbox
The bang path and "store and forward protocol" bit probably refers to mail routing in the UUCP days: http://en.wikipedia.org/wiki/UUCP#Mail_routing
That said, with a unique 'box' identifier and a simple store and forward protocol you could have them link together into a simple network, where you could pass messages or files with addresses like box1!box2!box3!userhandle :-)