Just released Last Defence for the PC - based on the 1981 arcade game Defender ; save the human colonists from the marauding alien hordes.
The game can be played with keyboard, (some) game controllers and can also be played with just the left mouse button.
So why control the game with just one button? Using just the left mouse button allows the game to be controlled by a switch - a large button that can be used by people with a motion-impaired disability, e.g. cerebral palsy, to play games that would otherwise be inaccessible to them because they are unable to use conventional controllers. Added to this are settings in the options menu to slow-down various aspects of the game, decrease damage from enemies, in order to make the game accessible for people with poor reaction time.
More info on switch gaming here: http://www.oneswitch.org.uk/
On the other hand, if you find it too easy, there's options to make it harder!
Free demo available here https://fusionforgedgames.wixsite.com/home/games if you want to try it out, full game is available for $0.99 in the Clickstore: https://clickstore.clickteam.com/last_defence