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Get most of your games on GOG.com to use in Porting Kit! GOG.com games are best tested the most and advised to use!
The free Portingkit is the main application of paulthetall.com
Download Portingkit
For all the (Windows) Steam games you own try use one of the 8 Steam Wrapper builds available in the Portingkit.
No guarantees that all games work. But the Steam games you will find on this website should work with one of them. If you notice a game which work great and isn't listed on this site let me know, so I can add the game in the list.