Amazon bought Twitch a while back - I've never been too interested in Twitch personally, I mean I watch a lot of gaming videos on YouTube, but those tend to be short-documentary style videos, or game reviews. Watching someone else play a game, and on a schedule like live TV rather than on-demand anytime... bad combination for me.
When I was playing World of Warcraft though, I found out that the modern way to manage add-ons for it is through the Twitch client (apparently Twitch bought Curse gaming, sometime before Amazon bought Twitch) - and that works quite well.
Then I found out that if you've got Amazon Prime you can "subscribe" to one Twitch channel per month for free - and apparently that benefits the person running the channel as if you had actually paid. So I went through and subscribed to some people I already liked from YouTube - RedLetterMedia (Previously Recorded), GiantBomb, Blame Society, Pushing Up Roses and others.
The most recent development with Amazon/Twitch is that they're now offering free games, like the PlayStation premium service - but apparently you get to keep the games forever (linked to your free Twitch account) even if you cancel Amazon Prime at some point.
For March they've got 4 or 5 free games - "Superhot" being the standout for me. April will have a new set of games, including "Tokyo 42", another one I've got on my to-get list.
They download through the Twitch client, because they're coming from Amazon's digital game service (a direct competitor to Steam) - so kind of annoying to have yet another game client thingy to deal with, but I've had no issues with the Twitch client, unlike EA Origin and fucking god damn shitty U-Play.
Short version: Got Amazon Prime? Get your free games through Twitch.