A key element of Spring is infrastructural support at the application level: Spring focuses on the "plumbing" of enterprise applications so that teams can focus on application-level business logic, without unnecessary ties to specific deployment environments.
It is open source, production quality, framework for developing RESTful Web Services in Java that provides support for JAX-RS APIs and serves as a JAX-RS (JSR 311 & JSR 339) Reference Implementation. It provides it’s own API that extend the JAX-RS toolkit with additional features and utilities to further simplify RESTful service and client development.
Apache Tomcat powers numerous large-scale, mission-critical web applications across a diverse range of industries and organizations.
An open source Java framework that focuses on making integration easier and more accessible to developers.
At Netflix, Karyon is a framework and library that essentially contains the blueprint of what it means to implement a cloud ready web service. All the other fine grained web services and applications that form our SOA graph can essentially be thought as being cloned from this basic blueprint.