The program is a bit old. I do not know (and have not read up on it enough to know) if the program is still being developed. His news page is pretty old (so is his ABOUT page). So, it is free ... for now ... and it just might stay that way.

OK! I just looked at the forum. Apparently the developer (only ONE man, btw!) is doing this app in his spare time. This means progress is and has been slow. However, according to the developer (and users there) it is NOT dead. So, if you are looking for a free modeler with some pretty advanced features, perhaps this one will float your boat.