Because of this design, Gaia can not only be run on Firefox OS devices, but on other operating systems and in other web browsers (albeit with potentially degraded functionality depending on the capabilities of the browser).
Third party applications onto the device installed alongside Gaia can be launched by Gaia.
Documentation about Gaia
Getting help from the community
If you're working with Gaia, or developing Gaia applications, there are community resources to help you!