UTAU isn't open source - it's freeware. Even redistributing the editor binaries requires permission (as dictated at http://utau2008.web.fc2.com/redistribution.h

UTAU isn't open source - it's freeware. Even redistributing the editor binaries requires permission (as dictated at http://utau2008.web.fc2.com/redistribution.html http://utau2008.web.fc2.com/redistribution.html). As far as I know there aren't any open source singing voice synthesis engines that have become particularly popular thus far.