It is not worth the effort to get poser models into 3dgs becouse it is illegal. Poser models can only be used for rendering art work and cannot be distributed in a game environment. Models have copyright just like everything else. I suppose it may be possible to get a game license for some of those models but it would be thousands of dollars. You could go through all the effort of converting a model for a personal project and probably nobody would notice but that is a lot of work for something that you cannot distribute!
There is no similar program that will work, they all have the same restrictions.
You might be able to use Poser to work on models you have created and then import into 3dgs, I have never tried it.
Really the only way to get models into a game is to build them yourself with Blender, Truespace etc, or buy them from freelancers or 3D shops.