1. [Spring framework](https://github.com/spring-projects/spring-framework) The Spring Framework provides a comprehensive programming and configuration model for modern Java-based enterprise applications -- on any kind of deployment platform. 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. License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0) , github's star - 5921, stackoverflow - more [100 000 questions](http://stackoverflow.com/questions/tagged/spring). 

1. [Google Guava](https://github.com/google/guava) The Guava project contains several of Google's core libraries that we rely on in our Java-based projects: collections, caching, primitives support, concurrency libraries, common annotations, string processing, I/O, and so forth.Requires JDK 1.6 or higher (as of 12.0). License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0) , github's star - 3813. 

1. [Apache Commons](http://commons.apache.org/) - Apache Commons is an Apache project focused on all aspects of reusable Java components.Commons Proper is dedicated to one principal goal: creating and maintaining reusable Java components. License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0). 

1. [Lombok](https://github.com/rzwitserloot/lombok) Very spicy additions to the Java programming language. Project Lombok makes java a spicier language by adding 'handlers' that know how to build and compile simple, boilerplate-free, not-quite-java code. License: [MIT](https://opensource.org/licenses/MIT) , github's star - 1540. 

1. [Puniverse Quasar](https://github.com/puniverse/quasar) Fibers, Channels and Actors for the JVM. [Hello World examples](https://github.com/Vedenin/useful-java-links/tree/master/helloworlds/1.1-common-frameworks-and-lib/quasar). License: Eclipse Public v1.0/[GNU Lesser 3](https://en.wikipedia.org/wiki/GNU_Lesser_General_Public_License), github's star - 1091. 

1. [Rootbeer GPU Compiler](https://github.com/pcpratts/rootbeer1)The Rootbeer GPU Compiler lets you use GPUs from within Java. License: [MIT](https://opensource.org/licenses/MIT) , github's star - 972. 

1. [Oblac Jodd](https://github.com/oblac/jodd) Jodd is set of open-source Java micro frameworks and tools; floppy size! Jodd = tools + ioc + mvc + db + aop + tx + json + html < 1.5 Mb. License: [BSD 2](https://en.wikipedia.org/wiki/BSD_licenses#2-clause_license_.28.22Simplified_BSD_License.22_or_.22FreeBSD_License.22.29), github's star - 912. 

1. [Google Jimfs](https://github.com/google/jimfs) An in-memory file system for Java 7+. License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0) , github's star - 752. 

1. [Spring batch](https://github.com/spring-projects/spring-batch) Spring Batch is a framework for writing offline and batch applications using Spring and Java. License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0) , github's star - 448. 

1. [Greenrobot common](https://github.com/greenrobot/essentials) General purpose utilities and hash functions for Android and Java (aka java-common). License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0) , github's star - 419. 

1. [Kilim](https://github.com/kilim/kilim) Lightweight threads for Java, with message passing, nio, http and scheduling support. License: [MIT](https://opensource.org/licenses/MIT) , github's star - 517. 

1. [Apache Isis](http://isis.apache.org) Apache Isis is a framework for rapidly developing domain-driven apps in Java. Write your business logic in entities, domain services and repositories, and the framework dynamically (at runtime) generates a representation of that domain model as a webapp or as a RESTful API. For prototyping or production. License: [Apache 2](http://www.apache.org/licenses/LICENSE-2.0).