The Apple ][ also (excluding the power supply IIRC) - this enabled the first wave of clones before the IBM PC (which also had the schematics included in the tec

The Apple ][ also (excluding the power supply IIRC) - this enabled the first wave of clones before the IBM PC (which also had the schematics included in the technical reference manual), but Apple managed to kill most of the clones due to copyright claims to the OS and BASIC (Woz’ Integer BASIC or the later Applesoft developed by Microsoft). The IBM PC BIOS was less complex than the Apple ][ OS+BASIC and back in the days Compaq commissioned a clean room reengineering of the BIOS to create legal IBM PC clones. So you only had to buy a copy of DOS (or CP/M-86…).