AutoTheory is more reasonably priced than AutoTonic. ($49 vs. $179)
Cales/Chordz are free 32-bit/64-bit VST plug-ins.
AutoTheory's scale and chord tools are synergistically integrated into one plug-in-agnostic MIDI driver application. AutoTonic is a plug-in-agnostic MIDI application. Cales/Chordz are two powerful, independent VST plug-ins.
Recommendation: Despite the overlapping functionality of these three tools, each one brings something different to the table. Unless someone figures out how to merge all of this goodness into a single MIDI tool, you will just have to own them all and use the one that best suits your current need at the time.