RxJava – Reactive Extensions for the JVM – a library for composing asynchronous and event-based programs using observable sequences for the Java VM.

A libre lightweight streaming front-end for Android.

High Performance Inter-Thread Messaging Library

Very spicy additions to the Java programming language.

Modifications to the Minecraft base files to assist in compatibility between mods. New Discord: https://discord.minecraftforge.net/

Catch common Java mistakes as compile-time errors

Java 1-21 Parser and Abstract Syntax Tree for Java with advanced analysis functionalities.

Reformats Java source code to comply with Google Java Style.

Keep your code spotless

The missing bridge between Java and native C++

Google Go language IDE built using the IntelliJ Platform

Java bytecode engineering toolkit

Log analyser / visualiser for Java HotSpot JIT compiler. Inspect inlining decisions, hot methods, bytecode, and assembly. View results in the JavaFX user interface.

FST: fast java serialization drop in-replacement

BuildCraft

A sampling JVM profiler without the safepoint sample bias

A Minecraft plugin API

Libre Minecraft mappings, free to use for everyone. No exceptions.

Support alternative markup for Apache Maven POM files

Fabric's mostly-version-independent mod loader.

A fast and small JSON parser and writer for Java

Minecraft mod development framework used by Forge and FML for the gradle build system

Infinite* height mod for Minecraft

Redstone Engineering

Source code for Forestry (Minecraft mod).

QDox - full extractor of Java class/interface/method definitions (including annotations, parameters, param names)

Android e-book reader with cloud synchronization

Open source, multithreaded, voxel game engine and platform, written in Java.

Distributed Fault-Tolerant File System

A port of Github's Refactoring tool Scientist in Java