CMU Coke machine
A soda machine at Carnegie Mellon that, from 1982, could be asked over the network whether it had cold bottles — often called the first internet-connected appliance.
The computer science department's machine stood some way from most offices and was restocked with warm bottles, which took a couple of hours to chill. Walking over to get a lukewarm Coke, or none at all, was annoying enough that a few students and staff wired microswitches into each column, read by the department's computer.
From then on anyone on the ARPANET could run finger coke@cmua and see how many bottles each column held and how long they had been there. Utterly serious in execution and utterly frivolous in purpose — which is roughly how the Internet of Things would feel decades later.