Fabrizio Poce of June74 Software has released J74 Progressive, a toolset for chord progression making and harmonic editing in Ableton Live and Max for Live.
While very well equipped for the actual performance, Ableton Live does not provide any specific harmonic editing capabilities: you cannot ask Live to suggest a chord, if your are building a progression or if you imported a clip you do not have a tool to find out which scale that clip is in. Actually you do not have any notion of chord or scale in your material while editing in Live MIDI editor.
The J74 Progressive toolset targets exactly these topics. Progressive is a sophisticated tool for harmonic editing. It is capable of producing high quality chord progressions and arpeggios directly as MIDI clips and provides tools for scale and chord detection as well as MIDI clip harmonization.
Progressive is available to purchase for $12 USD. Requires Ableton Live 9 or higher, with Max for Live.