Tizen OS, Firefox OS, Sailfish OS, Ubuntu Touch. These are the names of four new mobile OSes that have just been launched or are about to be. They all support touch interfaces.
Tizen OS is open source. Tizen runs Tizen-apps, web- and hybrid apps. Parts of Samsung's Bada OS, which is about to expire, will be added to Tizen.
Ubuntu Touch is open source. It currently runs on Nexus Android sets and it can run Ubuntu Touch-apps and web-apps. A good number of interesting games run on Ubuntu and then presumably on Ubuntu Touch too.
Sailfish was started by former Nokia employees. It runs Sailfish-apps, Android- and web-apps. The UI (user interface) can be customized to a high degree.
Firefox OS comes from the browser company. It can run Firefox-apps and web-apps. Of the four new OSes, Firefox OS is the one closest to launch.
One might ask what is the point of so many mobiles OSes. I think it has to do with the app-concept. There are different ideas of what an app should be. Some think Apple's proprietary app-concept is unnecessary and claim that web-apps written in HTML5 can do anything iOS-apps can do.
Then there's Sailfish, which owes its existence to developments within Nokia, the demise of its Symbian OS and the MeeGo OS. Some Nokia employees thought there was more mileage left in MeeGo and built Sailfish.
The competition in mobile OSes that these OSes seem to promise, is likely to bring great consumer benefits.
Cheap hardware already exists and will bring more phone makers. I can imagine Facebook as a phone maker and that they might adopt one of the new mobile OSes instead of Android or in addition to Android. Other likely phone makers are content owners, the ones that already have tablets.
I've tried a few web-apps and I don't think they are ready to take on Apple's iOS apps yet. In a few years they probably will, but that is several iPhone generations from now.