Newsbrief: Facebook announced a Messenger Platform at F8 this week, allowing developers to create apps to be used from inside Facebook Messenger on mobile.
While there has been no mention of any game apps at this point, there's no reason the platform couldn't grow into something akin to the games distribution platforms that popular mobile messaging apps like WeChat and LINE have become.
Facebook's new Messenger platform seems simple enough, with users installing the relevant apps from within the messenger itself.
Currently the suite of apps is focused around the use of gifs and voice/image manipulation, and more information about what's involved with developing for the platform can be found on the Messenger section of Facebook's developer hub.