JMRI stands for Java Model Railroad Interface and includes both Decoder Pro and Panel Pro software. It enables you to control your loco (Decoder Pro) and / or your layout Panel Pro from your PC.

 Java interfaces and sample implementations for controlling a model railroad layout from a personal computer. JMRI is intended as a jumping-off point for hobbyists to build their own layout controls. Includes the DecoderPro and PanelPro applications.

Sourceforge is the best site to download from as they guarantee no additional or unwanted software comes with it