NullpoMino - NullpoMino is an open-source action puzzle game that works on the Java platform.
Netbeans - NetBeans IDE 7.0. Develop desktop, mobile and web applications with Java, PHP, C/C++ and more. Runs on Windows, Linux, Mac OS X and Solaris. NetBeans IDE is open-source and free.
Blockinger - An open source Tetris clone for Android.
Eclipse - Eclipse is an open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle.
Good Old Tetris - Play Tetris Online. The game that will never get old.
IntelliJ IDEA - Capable and Ergonomic IDE for JVM