Learn the basics of Firefox OS, your alternative to Android and iPhone, at the offical web site, mozilla.org
When the iPhone was first released, there were no apps made by any companies. (Apple was the only one permitted to make apps.) Companies were expected to develop mobile web apps using HTML5, CSS, and JavaScript. (I call these HTML+2, the industry uses the general term of Web Apps.)
Hackers decided to make apps for the iPhone anyway, and Apple figured they might as well get 30% of the sales, so the AppStore was born.
Although we commonly have "iPhone apps" and "Android apps" you can still create web apps which will run on both these devices plus in addition they'll run on the new Firefox OS. You need to tweak the code to get it to work on all three, but it's better than having to program one app three times.