We have created a sketch-based combined modeling and rigging tool that we'd love for you to try. We call it RigMesh.
It is sketch-based, meaning that you create shapes by drawing the silhouettes of parts. The parts are automatically rigged with bones and skin weights. You model by attaching parts together (merging) and cutting them apart. You can also pose and deform the model or its parts with inverse kinematics. (...)
RigMesh is a research prototype, so it lacks most of the "polish" of commercial software.
Download it from here
All the usage instructions can be found in the readme in the download...
It even exports to FBX...
Full announcement over at cgtalk
Seems like a nice way to spend a "lazy sunday afternoon"... ;)