A few comments on the ABC bits of this.

The problem I had with ABC Navigator was with key signatures. For a lot of ABC on the web, the signature may be in the form
K: E Dorian
with a space. ABC Navigator ignores everything after the space, so your tune is processed as if it were in E major. Since this way of writing key signatures ais standard ABC and has been in use for many years before ABC Navigator came on the scene, there was no excuse for it.

The ABC to Lilypond converter screws up in the same way. At least the people involved in that will respond and acknowledge that there's a problem, though they can't fix it just now. Write to the developer of ABC Navigator and you get no acknowledgement whatever. As far as I'm concerned, that attitude means a piece of software is dead.

MIDI conversion: both the converter sites mentioned here use abc2midi. This interprets dotted constructs (as in strathspeys) with a 2:1 time ratio. This is just plain wrong. The implementor thought it was a good idea for hornpipes (which it often is) but instead of making 3:1 the default and interpreting an
R: hornpipe
line to get 2:1, we get 2:1 for everything. Sounds bloody stupid for almost all music. This can be fixed, either by editing the source or by setting switches at runtime, but neither site does it.

Folkinfo's transposition service is both very hard to use and limited in its output. You have to specify the transposition by counting semitones. I just tried it, transposing something from F major to D major. How many semitones is that? Not being a guitarist, I DON'T HAVE A FRIGGIN CLUE, and had to count on my fingers. I could have transposed the music at sight on any of a dozen instruments, but none of them have frets. If you aren't a guitarist you don't think that way, you may well think "F is four fingers and a thumb, D is six fingers and a thumb" or something similarly instrument-specific in a different way. Instead, "source: F; target: D" is something everybody can understand. (Semitone counting also fails to distinguish between transposing to C sharp and to D flat - if you're doing it at all, the distinction will matter).

Also, what I wanted was transposed ABC source. Folkinfo gives you only a transposed MIDI or PDF score. Far better to offer *only* source-to-source transposition and let people re-enter the transposed source if they want something other than ABC - it only takes one more "copy, paste, push button" sequence to get it.

ABC2WIN: this program is a disaster. The implementor didn't bother keeping it up to date with improvements to the ABC spec even when it was payware. If it's now free, you are getting a *lot* less than you paid for. Even very basic ABC features like staff breaks, beaming and tempo are utterly fucked up. You can tell tunes that were entered with it because they all sound like funeral marches and display as a jumbled mess unless you spend a significant amopunt of time editing them.