Pivotal/VMware's Java framework — the JVM equivalent of Rails/Django. Anchors a huge chunk of enterprise backends.
From Wikipedia
Spring Boot is an open-source Java framework used for programming standalone, production-grade Spring-based applications with a bundle of libraries that make project startup and management easier. Spring Boot is a convention-over-configuration extension for the Spring Java platform intended to help minimize configuration concerns while creating Spring-based applications. The application can still be adjusted for specific needs, but the initial Spring Boot project provides a preconfigured "opinionated view" of the best configuration to use with the Spring platform and selected third-party libraries.