StarMouse by Investronica
The StarMouse by Investronica was a one-button mouse with an iron ball. It plugged in to the QL's CTRL2 port and also the ROM expansion port (only for its power supply). The StarMouse only works on a QL with 128K RAM. It came bundled with a paint package and could only be used with that software. It was a sales flop in Spain and although a launch was planned in the UK, I'm not sure if it ever happened.
The Spanish software that originally came on an unlabelled microdrive cartridge is here (page in Spanish, StarMouse software is under 'Utilidades'):
Abel Ruiz wrote the software and there is a Spanish language account of his development work here:
http://sinclairql.speccy.org/articulos/historia/starmouse.htm
Here is a 1988 review (in Spanish) on the purchase and use of the StarMouse:
http://sinclairql.speccy.org/articulos/hardware/escarabajo.htm
Title: StarMouse
Interface Type: Mouse
Connection: Sinclair QL Joystick Port and QL ROM port
Through-Connector: NO
Manufacturer: Investronica
Year First Sold: 1985
Original Price: 7,500 Pesetas and eventually reduced to 1,500 Pesetas
Download Manual: n/a
Accompanying Software: Bundled Paint-type package