portmidi-rs provides portmidi bindings and the latter one is available for linux/mac and windows.

Provide a control layout for TouchOSC.

Wait until the initialization process is finished before starting the audio backend.
The init process includes the following tasks:

• calculate wavetables
• setup the MIDI and OSC receiver
• prepare the ring buffer
• future addons:
  • prepare websocket for web GUI
  • load configuration

Add --voices argument and start multiple oscillator threads for each voice.

Investigate if the iterator usage pattern is more rusty because mpsc channels implement FromIterator and therefore provide iter().

Docopt adds a dependency rustc_serialize and won't give much control about the naming of the CLI flags. It does a bit too much magic for my taste.
clap is a quite normal argument parser with an API that looks a bit like python's argparse, which I like to use.