Melodyne offers many more features like i.e. DNA (direct note access) into polyphone material and is available as a plugin for industry leading DAW / studio software platforms. NewTone just allows to manipulate monophone material (like vocals or single monophone instruments).
Melodyne work's on an very own patented mathematical algorithm which is'nt available over other products / solutions and offers the naturalst results in the market. Afaik it IS till the market leader in this segment. For monophone material AutoTune from antares is the most known "auto tune" and pitch correction / manipulation tool by history, but there exist many other products today offer pitch and time correction facilities in any way and in (very) different qualities but afaik melodyne is still the indutry standard on a profesional level.