Facebook's Instant Games technology hasn't exactly taken off (there are less than 200 games to date), but that's because it's been in closed testing. Now, it might have a chance to grow: Facebook has opened the Instant Games platform to all developers. Anyone can build HTML5-based web games designed to run in Messenger or your News Feed, whether you're on desktop or mobile. They'll have ways of making money from and promoting games, too, including ads (sorry, folks) and cross-promotional links.
Creators don't have to start from scratch: Facebook already has a number of recommended game engines to use with the platform.
Games have clearly been a mainstay of Facebook for a long while. The Instant Games tech is really a logical extension of the social network's strategy. It makes games (and importantly for Facebook, the ads that run alongside them) available in more places, and eliminates the long load times you sometimes see with more conventional games. No, this isn't likely to upend the conventional game market, but it could make gaming decidedly more accessible.