This series of apps for Macintosh are designed for those who used to touch-type and lost the use of one hand.
One-Hand Keyboard lets you type the good-hand equivalent of a letter your bad hand would normally type and uses lets the computer figure out what you meant to type. So for example, instead of typing 'this', you would type 'tges' using mirror equivalent of keys you would normally type with your right hand. The computer figures out what you want to say. Apparently the substitution is easy to learn, but I reserve judgement.
The app is fairly expensive, at 133.99, but there is a cut-down free version for free practice and testing the application.
There is also a free application (Mirror-QWERTY), where you need to press the space bar every time you type the equivalent letter to let the computer know what you mean.
Well worth exploring for those who lost the use of one hand and want to do some typing.