I'd love it if there was a KIP/MacIP based package that you could use on a Mac 512K (no, a 128K will never cut it) to access a Unix box. I've tried it, and I have exchanged mail with the developers who tried in the 1980s, but nobody can locate the source code for those efforts. From a basic IP stack, you could create apps that are more Mac-like than Contiki by driving command line Unix apps on a server.

It might also be possible to cobble together a UUCP for Mac OS X internal gateway and a vintage Mac front end. The problem would locating external UUCP exchanges that connect to the modern internet.

It's like running a 1910 Stanley Steamer on the road today: the machine may work and it may run at a reasonable pace, but the modern world doesn't provide regular coal and water refuelling points.