FrostWire is a file sharing client and media management tool that was made using lots of cool open source projects. It was born from the legendary LimeWire Gnutella client, but it's evolved a hell of a lot since then.

FrostWire no longer supports Gnutella,** it's a BitTorrent client, an Internet Radio client and Media Player.**...

Geotoolkit.org is a free software, Java language library for developing geospatial applications. The library can be used for desktop or server applications.

Geotoolkit.org provides data structures for geographic data and associated metadata along with methods to manipulate those data structures. The library rests on a set of utility classes which include a framework for factory classes along with extensions to the Java language....

vert.x - Effortless asynchronous application development for the modern web and enterprise

Kalypso is an open source application for geospatial modelling and simulation. It is primarly developed to be a user friendly tool for GIS-based modeling and simulation of hydrological and hydraulic numerical models.

Querydsl is a framework which enables the construction of statically typed SQL-like queries. Instead of writing queries as inline strings or externalizing them into XML files they can be constructed via a fluent DSL/API.

The benefits of using a fluent API in comparison to simple strings are...

The Java bindings for GTK and GNOME! Featuring a robust engineering design, completely generated internals, a lovingly crafted layer presenting the public API, and steadily increasing coverage of the underlying libraries.

You can use java-gnome to develop sophisticated user interfaces for Linux applications so that they richly integrate with the GNOME Desktop while leveraging the power of the Java language and your expertise with it....

Cosmo (Chandler Server) is a Java-based content/calendar sharing server with a built-in rich web application client.

eFaps is a framework used to map objects with or without attached files to a relational database and optional file systems (only for attaches files).

A generic next-generation Java library for image processing,

Sentry is a realtime event logging and aggregation platform. It specializes in monitoring errors and extracting all the information needed to do a proper post-mortem without any of the hassle of the standard user feedback loop.