Grape
An opinionated framework for creating REST-like APIs in Ruby
...It integrates well with frameworks like Rails or Sinatra but can also be used standalone for microservices. Built-in tools like parameter coercion, strong validations, and automatic documentation (via Swagger integrations) reduce boilerplate and improve maintainability. Because it’s lightweight and purpose-built, Grape is popular in service-oriented architectures where clean, well-structured APIs are central.