NuVinci
I had read a lot about the NuVinci drive, and a few months ago when the rear wheel of my Trek disintegrated (long story), I decided to convert it.
I had no idea what I was getting into; I thought that it would be a simple matter. My LBS promised to research it.
After a couple of months, my LBS owner has just e-mailed me to the effect that the bike will be ready next week. Stand by for a report.