JMRI (Java Model Railroad Interface) is an open source program (GNU GPL v2) for model railroad hobbyists. It allows users to control leds, horn, or switch the railway of hobbyist open source or commercials closed sourced trains.
JMRI is a suite of tools distributed via a single download. The two most popular tools are DecoderPro for programming DCC decoders, and PanelPro for controlling layouts.
Starting in 2005, Bob Jacobsen, the JMRI project administrator, was involved in a legal dispute with Matt Katzer in the United States District Court for the Northern District of California. The Court of Appeals for the Federal Circuit made an important ruling that infringing on the copyright of open source software by violating its license terms could result in monetary damages. The case settled in early 2010.