Amazon Prime members can play 4 different Luna cloud games for free, as much as they want, through September 15. The available free games are Metro Exodus, Resident Evil 7 Biohazard (Gold Edition), Katamari Damacy REROLL, and Monster Boy and the Cursed Kingdom. An invitation to Luna is not required. Just launch the Luna app on a Fire TV, Fire tablet, or compatible browser/PC/phone and start playing.