You should take a look at Blender, open source and also provides really good renders and animation tools.
Zbrush is good for morphs and high detailing. It is a valuable tool but is mostly used in conjunction with other modeling programs.
They can all work with Poser but you need to find and stick with a work flow. As someone else has mentioned there is an inter poser plugin, how well it works I don't know. Mostly you will have scaling and material issues...they are usually easy to overcome though.

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