I mostly use 3d modelling software myself. DesignDoll is a personal favourite of mine, but it was already mentioned. It's limited in two ways, however: The anatomy is very much cartoon / manga style, and the free version does not allow you to save your models (so once you customize a doll, you need to take a complete photoshot in one go).
MakeHuman has some incredible customization options, including age (from child to elder), a large variety of body builds, adjustable pregnancy, ability to customize each body part as you please (great for creating grotesque models!). However, it's got no posing of its own - you need a third party software like Blender to use your models. I know there are some other programs, but I found them too complicated and feature-heavy to use for reference.
I hope that helps!