[gnufx]

Tasteful. LSI-11 for the likely cheapest PDP (though we weren't -11 fans)?

X.25 may have been legendary, but certainly not mythical! It was what the UK academic network ran on long ago, and worked well, but was steamrollered by IP (which ran over it for a while). I was rather surprised at how primitive computing/networking was at the US equivalent lab when I spent a summer there. I wouldn't know where to look for kit now, but it's surprising what lurks in the bowels of academic establishments! I've seen suggestions it's still in use in other environments. There was something of a competition for the most obsolete bits found by out Field Support.

Edit: There's probably assorted X.25 in Jim Austin's collection, specifically on the GEC 41xx: http://www.computermuseum.org.uk/