...I can perform keyframe animation on Animata bones, joints, and layers, by creating and manipulating Ruby objects. I've implemented support for all of the parameters for which Animata currently allows OSC control, and confirmed that it would be trivial to add more OSC parameters to Animata in the future.
The next step is to create a GUI. After attempting to get the FLTK bindings for Ruby installed (which failed because FL/glut.h is missing from Ubuntu's FLTK developer package), I attempted to use wxRuby. This failed because Ubuntu's wxWidgets package is built without one of the libraries upon which the wxRuby gem depends. I could have rebuilt FLTK or wxWidgets from source, but I don't want other people to be required to jump through such hoops if they want to try OSCimator.
Consequently, I've decided to use Tcl/Tk for the GUI, since the Ruby bindings are readily available for all major platforms. It remains to be seen how steep the learning curve will be, but I'm encouraged by how quickly OSCimator's core classes came together.