I’ve been working on IDN-OSS for a few months now. Although we have yet to produce a usable product suitable for the general audience, we have just released an alpha-quality plugin for Internet Explorer 6 on Windows 2000/XP. There is also a simple IDN conversion tool for Windows.
There is still a lot of work to be done, so I will continue to work on the client for the next couple of weeks to bring it to the masses. Stay tuned!