EDSAC, first run in 1949 and presently being recreated at TNMoC, was certainly a room-sized computer but has been remade in pocket size by David Boucher. Here’s his Hackaday project page and here’s a nice explanatory video:
There is an EDSAC emulator written in BCPL by Martin Richards. (Along with some papers, and programs). It’s probably no coincidence that MR studied/worked in Cambridge where EDSAC was built…
I’ve attached a poster from Cambridge about it.
Actually, can’t attach due to this place not liking PDF, however
That’s a nice poster! Also of interest, perhaps, there’s an in-browser emulator for EDSAC here.