here a couple more usefull trackers (these use generated sounds instead of samples):
https://code.google.com/p/klystrack/
http://www.delek.com.ar/deflemask
The later is new to me, but seem to have this nice feature:
If you are writing a music app and you want to include DefleMask support, you want to convert any format to the DefleMask format or transform a DMF to a different filetype, this will be helpful: DMF Format Specs( http://www.delek.com.ar/soft/deflemask/DMF_SPECS.txt), DMP Format Specs(http://www.delek.com.ar/soft/deflemask/DMP_SPECS.txt).