The JMRI Throttle Tool is just one of the many digital railroading tools that are part of the JMRI Project. It has the ability to run a DCC decoder equipped Locomotive around a layout using a computer keyboard and mouse for control instead of a hand-held throttle. The Throttle tool offers many of the same features that can be found on most hand-held throttles, including the ability to control light and sound functions.
See also:
And for a related topic:
Throttles Help for JMRI v 1.x/2.x