Twitch is offering FIVE games free to Twitch Prime users, with more on the way next month and beyond. More info at Twitch blog (click)
Superhot (Steam Link)
Oxenfree (Steam Link)
Mr. Shifty (Steam Link)
Shadow Tactics (Steam Link)
Candlekeep: Tomb of Annihilation (Steam Link)
note: Steam links are for info purposes only. Steam keys are not given, rather the games must be downloaded through the Twitch client (more info at Twitch blog link above)