The Altair 8800 didn't have great usability by modern standards. Released in 1975, it arrived as a kit that had to be assembled, and could only be programmed and interacted with via a series of switches and lights on the front panel. Nevertheless, as the first commercially successfully personal computer, it's generally regarded as having kickstarted the microcomputer revolution. Blockchain is roughly as usable today as the personal computer was in 1975, but it's improving by leaps and bounds.
This is a companion discussion topic for the original entry at https://www.etherean.org/blockchain/design/ux/2020/10/17/key-ingredients-better-blockchain-part-viii-usability.html