Spring Framework
Java framework for dependency injection + enterprise services. Rod Johnson, 2003 (after the book "J2EE Design and Development"). The most-used Java stack after the standard JDK.
Pitch: alternative to heavyweight J2EE application servers (WebSphere, JBoss). IoC container + AOP + JdbcTemplate + transaction management. Spring Boot (2014) revolutionized: convention over configuration, embedded Tomcat, one jar → production. Pivotal owns it (since VMware → Broadcom 2023). Spring 6 (2022) + Boot 3 require Java 17+, support native AOT via GraalVM. Competitor: Quarkus (Red Hat, native-first), Micronaut.