You keep using the word tone but I'm not sure you know what it means. Recorded audio produces a wavelength full of crests and troughs containing a wide range of unique harmonic information. Auto tune just takes that information and modulates the pitch to the desired note. Absolutely nothing about the quality of the tone or timbre is altered in any way shape or form. There are ways to alter the structure of the original waveform changing its harmonic integrity thus altering its timbre, but that is not what anyone who knows anything about audio recording uses autotune for. That's called additive or subtractive synthesis. The company that makes the software even calls it a pitch correction tool.
Antares Auto-Tune is the “real” one. GSnap is a free VST plugin that claims to do the same thing. Autotalent is a LADSPA plugin that should work on Linux.