The Restlet website defines the framework as the Leading Java Framework for building APIs (if I remember that correctly) and for a time Restlet was very much active in the community. After the acquisition of Talend, it seems the direction of Restlet has changed.
Furthermore, Restlet compared to other Java frameworks seems to be lacking modern features that an adequate number of applications (if not most) needs, WebSocket, non-blocking I/O, and reactive features missing in the framework and it seems it is quite lagging compared to other frameworks. Some important features that are either not implemented for quite a long time or just unplanned for the core developers.
The question now, in terms of programming, is it still reasonable (today) to invest in developing applications using the Restlet framework or it is much better of picking up frameworks like Vert.x or Quarkus (JAX-RS) or Spring instead?