Just to bang on again about HARMONY!

It can do most what is listed above (including Transpose).
It provides alternative input methods via keyboard or drag and drop
It does handle triplets correctly (and other tuples)
It can import MIDI melody (with some restrictions) and abc
It can add chords automatically - this was the whole point of it.
It provides Guitar Staff where all parts are shown in the Treble clef


I have been trying to make it easy to use, and would welcome futher suggestions along these lines.

Only available on Windows though, because I wrote it in VB. Rewriting in C (or Java) is NOT an option for me (Any volunteers?)