there's this repo and it still seems to be maintained. I was following this project when it first started and tried it for a while it seems pretty solid.
Interesting - they don't seem to publicize this at all on their site, nor do they mention the LGPL anywhere (that I could find). Their site only seems to offer it under an EULA.
I wonder if these LGPL sources are the full source of the application, then.
edit: prior revision of the readme clarifies that, although the Plasticity source code is LGPL, it uses a proprietary library which makes the resulting product proprietary. Presumably the expensive licenses are for this proprietary library and not for Plasticity itself. This proprietary library seems to be Parasolid, the geometry kernel. I wonder if there is a fully free alternative.