The Reaktor provides a complete backend for running a digital reading ecosystem. txtr.com is using the reaktor as a backend, and so do many more digital reading sites (and apps) all over the world.
Reaktor functionality includes catalog access, checkout, eBook upload, storage ("vault"), download,
metadata management, access rights management, presentation, discussion, search, and more.
The Reaktor API has two components: The RPC (remote procedure call) part and the delivery part.
Delivery is dealing with binary data, that is: Upload and download of documents.
RPC is dealing with everything else.
The delivery component is always accessed through simple HTTP requests.
The RPC API can be accessed through SOAP, REST, or JSON.
SOAP, REST and JSON aren't different APIs, but merely three different kinds of encoding remote procedure calls.
For information on how to get access to content, see the catalog API page.