I remember making an engine incredibly similar to this. It was intended for an RTS back in 2004, and you'd select a unit by left clicking them, and tell them where to move or who to attack by right clicking a place on the screen. It wasn't very hard to make.

I assume this engine comes from the ancient times before version s1, though, where mouse input didn't exist. This engine is an interesting glimpse at the old days, but is an incredibly clunky engine (see the screenshots), even for something probably made in MZX 2.51, making it practically useless in any sort of application. Two stars for effort, though.