Free to use on PCs, is the very natty Switch Viacam. It enables two switches to be mapped in thin-air. Imagine a webcam displaying a live image of whatever it's pointing at, where you can map out one or two boxes within that space. If anything passes through those boxes, or moves within them, a switch function is activated, such as an emulated left-click.
It works very well for some activities, although sadly not on games consoles through a Cronus Max. This is a brilliant idea, much like the OAK Air Switch, and free is my favourite price.
Created by the talented Cesar Mauri Loba and the APPC of Tarragona, see also the webcam based head-tracker with dwell clicking: Enable Viacam, and Cause and Effect fun with SITPLUS.
Many thanks to Will Wade and Gillian Taylor of SpecialEffect for this info. Added to the Accessible Gaming Shop switch and software sections.