Is this a reader or an editor?

It was originally a reader only. As of b35, you can write/edit screenplays too using the Fountain format.

In b36, an importer was added to turn FDX (Final Draft) scripts to Fountain. And you can now export from Fountain to .FDX or .HTML..

In b43, the ability was added for Android version 4.4 or higher to print to a PDF file or a cloud printer.