K-2 Electronics Design offered a particularly robust keyboard upgrade to the ZX-81/TS-1000, one that far exceeded the options available from many other manufacturers at the time.
The Kradle was more than just a keyboard upgrade: it included an expansion card with 64K RAM, a joystick port, cassette signal conditioning, extra automatically shifted keys and several other features.
As upgrades go, it was an attractive package. And that was not all: two further upgrade options gave an RS-232 and parallel input/output ports. The latter was adaptable to drive parallel printers.
