If you have Amazon Prime (and the included Twitch Prime), you can download this month the games Hacknet: Complete Edition, Poi and Smoke & Sacrifice.
And after the awesome Metal Slug 3 (July) they added further classic SNK games this month: Baseball Stars 2, Fatal Fury Special, Metal Slug 2, Pulstar and Samurai Showdown II
You can keep all Twitch Prime games even after the Prime subscription ends.