* [Apache Maven](http://maven.apache.org/) - Declarative build and dependency management which favors convention over configuration. It might be preferable to Apache Ant which uses a rather procedural approach and can be difficult to maintain.

* [Bazel](http://bazel.io) - Build tool from Google that builds code quickly and reliably.

* [ASM](http://asm.ow2.org/) - All purpose, low level, bytecode manipulation and analysis.

* [Byte Buddy](http://bytebuddy.net/) - Further simplifies bytecode generation with a fluent API.

* [Byteman](http://byteman.jboss.org/) - Manipulate bytecode at runtime via DSL (rules) mainly for testing/troubleshooting.

* [Bamboo](https://www.atlassian.com/software/bamboo) - Atlassian's solution with good integration of their other products. You can either apply for an open-source license or buy it.

* [CircleCI](https://circleci.com/) - Hosted service with a free trial.

* [fabric8](http://fabric8.io/) - Integration platform for containers.

* [Jenkins](http://jenkins-ci.org/) - Provides server-based deployment services.

* [TeamCity](http://www.jetbrains.com/teamcity/) - JetBrain's CI solution with a free version.

* [Travis](https://travis-ci.org) - Hosted service often used for open-source projects.

*Efficient and specific data structures.*

* [Protobuf](https://github.com/google/protobuf) - Google's data interchange format.

* [SBE](https://github.com/real-logic/simple-binary-encoding) - Simple Binary Encoding, one of the fastest message formats around.

* [Wire](https://github.com/square/wire) - Clean, lightweight protocol buffers.

* [Apache DeltaSpike](https://deltaspike.apache.org/) - CDI extension framework.

* [Dagger2](http://google.github.io/dagger/) - Compile-time injection framework without reflection.

* [Immutables](http://immutables.github.io/) - Scala-like case classes.

* [JHipster](https://github.com/jhipster/generator-jhipster) - Yeoman source code generator to create applications based on Spring Boot and AngularJS.

* [JRebel](http://zeroturnaround.com/software/jrebel/) - Commercial software that instantly reloads code and configuration changes without redeploys.

* [Spring Loaded](https://github.com/spring-projects/spring-loaded) - Class reloading agent.

* [vert.x](http://vertx.io/) - Polyglot event-driven application framework.

*Libraries and frameworks for writing distributed and fault-tolerant applications.*

* [Akka](http://akka.io) - Toolkit and runtime for building concurrent, distributed, and fault tolerant event-driven applications.

* [Apache ZooKeeper](http://zookeeper.apache.org/) - Coordination service with distributed configuration, synchronization, and naming registry for large distributed systems.

* [Axon Framework](http://www.axonframework.org/) - Framework for creating CQRS applications.

* [Hazelcast](http://hazelcast.org/) - Highly scalable in-memory datagrid.

*Tools which handle the distribution of applications in native formats.*

* [Bintray](https://bintray.com/) - Version control for binaries which handles the publishing. Can also be used with Maven or Gradle and has a free plan for open-source software or several business plans.

* [Central Repository](http://search.maven.org/) - Largest binary component repository available as a free service to the open-source community. Default used by Apache Maven and available in all other build tools.

* [IzPack](http://izpack.org/) - Setup authoring tool for cross-platform deployments.

* [JitPack](https://jitpack.io/) - Easy to use package repository for GitHub. Builds Maven/Gradle projects on demand and publishes ready-to-use packages.

*Frameworks that support the development of games.*

* [jMonkeyEngine](http://jmonkeyengine.org/) - Game engine for modern 3D development.

*Libraries that simplify JSON processing.*

* [Gson](https://github.com/google/gson) - Serializes objects to JSON and vice versa. Good performance with on-the-fly usage.

* [Jackson](http://wiki.fasterxml.com/JacksonHome) - Similar to GSON but has performance gains if you need to instantiate the library more often.

* [LoganSquare](https://github.com/bluelinelabs/LoganSquare) - JSON parsing and serializing library based on Jackson's streaming API. Outpeforms GSON & Jackson's library.

*Libraries that log the behavior of an application.*

* [Apache Log4j 2](http://logging.apache.org/log4j/) - Complete rewrite with a powerful plugin and configuration architecture.

* [Logback](http://logback.qos.ch/) - Robust logging library with interesting configuration options via Groovy.

* [SLF4J](http://www.slf4j.org/) - Abstraction layer which is to be used with an implementation.

* [Apache Spark](http://spark.apache.org/) - Data analytics cluster computing framework.

* [DeepDive](http://deepdive.stanford.edu) - Creates structured information from unstructured data and integrates it into an existing database.

* [Deeplearning4j](http://deeplearning4j.org/) - Distributed and multi-threaded deep learning library.

* [JSAT](https://github.com/EdwardRaff/JSAT) - Algorithms for pre-processing, classification, regression, and clustering with support for multi-threaded execution.

* [Weka](http://www.cs.waikato.ac.nz/ml/weka/) - Collection of algorithms for data mining tasks ranging from pre-processing to visualization.

* [Lanterna](https://code.google.com/p/lanterna/) - Easy console text GUI library similar to curses.

* [LightAdmin](http://lightadmin.org/) - Pluggable CRUD UI library for rapid application development.

* [OpenRefine](http://openrefine.org/) - Tool for working with messy data: cleaning, transforming, extending it with web services and linking it to databases.

* [jmxtrans](https://github.com/jmxtrans/jmxtrans/) - Tool to connect to multiple JVMs and to query them for their attributes via JMX. Its query language is based on JSON, which allows non-Java programmers to access the JVMs attributes. Likewise, this tool supports different output writes, including Graphite, Ganglia, StatsD, among others.

* [Kamon](http://www.kamon.io/) - Tool for monitoring applications running on the JVM.

* [New Relic](http://newrelic.com/) - Commercial performance monitor.

* [Takipi](https://www.takipi.com/) - Commercial in-production error monitoring and debugging.

* [Ebean](http://ebean-orm.github.io/) - Provides simple and fast data access.

* [EclipseLink](https://www.eclipse.org/eclipselink/) - Supports a number of persistence standards: JPA, JAXB, JCA and SDO.

* [Hibernate](http://hibernate.org/orm/) - Robust and widely used with an active community.

* [OrmLite](http://ormlite.com/) - Lightweight package avoiding the complexity and overhead of other ORM products.

*Tools for performance analysis, profiling and benchmarking.*

* [JMH](http://openjdk.java.net/projects/code-tools/jmh/) - Microbenchmarking tool for the JVM.

* [JProfiler](https://www.ej-technologies.com/products/jprofiler/overview.html) - Commercial profiler.

* [LatencyUtils](https://github.com/LatencyUtils/LatencyUtils) - Utilities for latency measurement and reporting.

* [Reactive Streams](https://github.com/reactive-streams/reactive-streams-jvm/) - Provide a standard for asynchronous stream processing with non-blocking backpressure.

* [Reactor](http://projectreactor.io/) - Library for building reactive fast-data applications.

* [RestExpress](https://github.com/RestExpress/RestExpress) - Thin wrapper on the JBOSS Netty HTTP stack to provide scaling and performance.

* [RestX](http://restx.io) - Framework based on annotation processing and compile-time source generation.

* [Retrofit](http://square.github.io/retrofit/) - Type-safe REST client.

* [Swagger](http://swagger.io/) - Swagger is a specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services.

*Engines which index documents for search and analysis.*

* [Apache Solr](http://lucene.apache.org/solr/) - Enterprise search engine optimized for high volume traffic.

*Libraries that handle security, authentication, authorization or session management.*

* [Apache Shiro](http://shiro.apache.org/) - Performs authentication, authorization, cryptography and session management.

* [Bouncy Castle](https://www.bouncycastle.org/java.html) - All-purpose cryptographic library. JCA provider, wide range of functions from basic helpers to PGP/SMIME operations.

* [Google Keyczar](https://github.com/google/keyczar) - Easy to use, yet safe encryption framework with key versioning.

* [Keycloak](http://keycloak.jboss.org/) - Integrated SSO and IDM for browser apps and RESTful web services.

* [PicketLink](http://picketlink.org/) - Umbrella project for security and identity management.

*Tools which substitute expressions in a template.*

* [Apache Velocity](http://velocity.apache.org/) - Templates for HTML pages, emails or source code generation in general.

* [Handlebars.java](http://jknack.github.io/handlebars.java/) - Logic-less and semantic Mustache templates.

* [Thymeleaf](http://www.thymeleaf.org/) - Aims to be a substitute for JSP and works for XML files in general.

* [Grails](https://grails.org/) - Groovy framework with the aim to provide a highly productive environment by favoring convention over configuration, no XML and support for mixins.

* [Ninja](http://www.ninjaframework.org/) - Full stack web framework.

* [Pippo](http://www.pippo.ro/) - Small, highly modularized Sinatra-like framework.

* [PrimeFaces](http://primefaces.org/) - JSF framework which has a free and a commercial version with support. Provides several frontend components.

* [Spring Boot](http://projects.spring.io/spring-boot/) - Microframework which simplifies the development of new Spring applications.

* [Spring](http://projects.spring.io/spring-framework/) - Provides many packages ranging from dependency injection to aspect-oriented programming to security.

* [Vaadin](https://vaadin.com/) - Event-driven framework build on top of GWT. Uses server-side architecture with Ajax on the client-side.

*Active discussions.*

* [stackoverflow](http://stackoverflow.com/questions/tagged/java) - Question/answer platform.

* [vJUG](http://virtualjug.com/) - Virtual Java User Group.

* [InfoQ](http://www.infoq.com/)

* [Java Code Geeks](http://www.javacodegeeks.com/)

* [Java, SQL, and jOOQ](http://blog.jooq.org/)

* [JavaWorld](http://www.javaworld.com/)

* [RebelLabs](http://zeroturnaround.com/rebellabs/)

* [The Java Specialist' Newsletter](http://www.javaspecialists.eu/archive/archive.jsp)

* [The Takipi Blog](http://blog.takipi.com/)