I've uploaded a bug-fix version. It should solve most of the problems exposed on this thread. I haven't been able to reproduce some of the problems stated by obesebear, I'm not getting that error saving models with new parts attached. Could you decribe better what you did? If possible, send me the files you used. Also I'm not having any problem with the transaprent color. Again, If posible provide files.
As for the features request:
-Show floor: Sure, I'll add it as soon as I can.
-Adding Animations: Well, ok, shouldn't be a problem. I don't know if the game will like that change, though.
-Export 3Ds: It shouldn't be too different from importing, but it's by no means a priority.
-Adding bones: I've got a feeling adding/removing bones would lead to serious problems. First of all it could be somewhat problematic interface-wise, but aso keep in mind it would mean changing a lot of animations. I'll take a look, but don't expect too much.