It is hard to say which is the PC game with the most versions, but surely Super Mario is one of them. There is a continual stream of games inspired by this great classic, as is the case with this Super Mario PC Challenge 6.
In Super Mario PC Challenge 6 you must guide Super Mario or Luigi through 40 levels, with the aim of rescuing the Princess (who, in difference to other Super Mario games, isn't shouting all the time). You also have to defend an important tower against the evil Bowser.
Through all the different levels in Super Mario PC Challenge 6 you have to pass screens under water, confront flying saucers, fight at night with very low visibility, run through the desert, through frozen lands, in the rain, in the jungle, etc.