This is a simple web front end for the FlatBuffers Compiler (flatc 2.0.0).
Clicking Download will get you a zip file including the original schema, that is especially convenient for languages that require multiple output files.
Feel free to also use the API directly if you wish (sorry, no documentation yet, but just use developer tools to see the request payload, it is really simple).
This awesome service is brought to you by Matias Ärje. Feedback form here.