After years of talking about a spiral-based curve editing tool, the provisional patent application is filed, and I've made an unpolished release of the stuff I have now. Brave souls can check it out to see what I've been talking about. Others among you may choose to wait until there's a release that's not quite as spartan.
I made a Mac build, but loading and saving is more or less not implemented (you can kinda make it work using the commandline, but it really needs a file dialog). Background images (for tracing) are not supported yet either.
The solver has also not been tuned for numerical robustness, so when you play around with it, you'll often see it fail to solve the spline. It does work reliably when the pattern plate represents a real font shape rather than random points, though.
It's free software (GPL), and patches for improvements are greatly appreciated.