I’ve come across all of these separately over the years, but I don’t see them listed in a search of this forum, so I thought to put a thread. found them here: http://www.brickmap.info/category.php
I’ve used brickr, you can load a 3D mesh image and it’ll generate a 3D lego model based off of it. It tries its best to account for interior structure but you’re kinda on your own if you choose to hollow the shape (it saves material and less weight though) haha just ask @greg about that tree…