FamiTracker is a free windows tracker for producing music for the NES/Famicom-systems. The interface is based on MadTracker and should be easy to use if you've been using trackers before. One of the features is NSF-file exporting. That allows music created in this tracker to be played on the real hardware, or even for for use in your own NES-applications. Some other features:

Full real-time emulation of all channels Internal PCM to DPCM-sample converter MIDI input devices are supported NTSC & PAL modes are both supported

Bug-reports, comments and suggestions are welcome. Source is available under the GNU General Public License.