Opium

Offers declarative, intuitive routing syntax similar to Ruby Sinatra, making endpoint definition straightforward with path parameters, as shown in the hello_world example with App.get and App.post.

Built on Rock middleware inspired by Ruby's Rack, enabling custom request/response processing and plugin development, demonstrated in the Reject_user_agent example for browser filtering.

Integrates Yojson for type-safe JSON serialization and deserialization out of the box, simplifying API development, as evidenced by the Person module with yojson_of_t and t_of_yojson.

Handles request/response body streaming via Lwt streams for efficient data processing, illustrated in the streaming_handler that uppercases content on the fly.

Uses cmdliner for configurable app execution with options like port and debug mode, enhancing productivity through command-line flexibility, as seen in the run_command examples.