Way back in the day (1985) I was figuring out how to do timeslicing on a 4MHz Z80, and once I had it working on multiple terminals I slung a simple MUD on it (Shades). Connecting it to a couple of modems (this was the days when BB's were the thing) got people playing, at which point British Telecom's Prestel/Micronet decided they'd like to run it on their system.

The demand was sufficient that it kept crashing the entire national network, and one of my prize memories from back then is the night I was working late in this huge multistorey BT building (Baynard House) in London stuffed with big cabinets filled with computers and modems, and as I was huddled over my little Z80 the double doors burst open and the shift leader stormed in, shouting "There is NO WAY I'm going to put up with your system taking down the entire network". So I looked down my little Z80 box, then looked up at the seried ranks of GEC computers in their 48U cabinets, and did my best to puzzled, in a "Who, little ole me?" kind of way.

Ok, so it was 1200 baud max per user but we did get up to 128 users spread over 2 Z80s, each with 256Kb bankswitched RAM and 2Mb hand-made RAM disks.

The rest of it is a long story but it's still around [0] and I know a few people on here remember it (fondly I hope - though I do still feel guilty about those bills!).

[0] http://games.world.co.uk/shades/