UTAU, or Vocal Synthesizer Tool UTAU formally, is a fan-made voice synthesis program.
Unlike Vocaloid and Vocaloid2 platform distributed commercially by YAMAHA, this is a free program. Another feature which differentiate UTAU from Vocaloid is that its platform does not have voice bank, except for the attached default bank known as "Defoko." In other words, UTAU provides only the voice tuning function and users have to download voice banks optionally.
Momone Momo is one of the banks which are available on UTAU. Her voice has a clear and soft sound. With the latest update called "Renzoku Ongen" (Sequel Voice Source) along with UTAU platform itself, the voice received more natural singing and this improvement made UTAU the worthy alternative of Vocaloid.