Raspberry Pi is a line of cheap ($25 or less) single board ARM computer very popular with hobbyists. There is a $5 model with 32-bit ARM and 256M ram. But I have the PI3 and PI4 64-bit models ranging from 1G to 8G ram. Three in production, one as a UPS monitor and Wifi router (connecting to clearnet through a mesh network), one as a Bitcoin miner, one with 8G ram as an ARM build machine and potential desktop (attach to back of monitor).

One of these days, I'll hook up a $5 Pi with a moisture sensor and a speaker so that house plants say "I'm Thirsty!" out loud. It's all about giving a voice to the voiceless.