Hauptwerk is a computer simulation of a pipe organ for the PC, playable by MIDI. Different pipe organs can be loaded into the program and you can sample and create your own. It differs from most software synths and samplers in that a large (3-5 second) sample is loaded for every pipe in the organ, which may amount to several thousand samples and several hours of audio, but gives extremely realistic results.

The default download includes a test organ with a single pipe. To use the program you will also need to do download a set of organ files. Those files are exetremely large downloads. You can also purchase the program, complete with organ files on a CD.