Acorn Archimedes
British home computer from 1987 and the first built around an ARM processor — the same architecture now inside nearly every phone.
Acorn, maker of the BBC Micro, couldn't find a CPU it liked for its next generation, so it designed one. The ARM2 was a small RISC chip with around 30,000 transistors, and in the Archimedes it ran roughly twice as fast as contemporary 68000 machines. The operating system shipped as Arthur and was soon replaced by RISC OS.
The machine did well in British schools and barely anywhere else; games were scarce and the price high next to the Amiga. The processor was what survived. ARM was spun off as its own company in 1990, and the rest is mobile history. A small demoscene showed early on what a fast CPU with no custom chips could manage: everything had to be done in software, and it worked.