A real professional free modelling system is K-3D, available for Windows, Linux, Apple: http://www.k-3d.org/wiki/Main_Page

From K-3D's Wiki:

K-3D is the free-as-in-freedom 3D modeling, animation, and rendering system for GNU / Linux, Posix, and Win32 operating systems. K-3D features a robust, object-oriented plugin architecture, designed to scale to the needs of professional artists, and is designed from-the-ground-up to generate motion-picture-quality animation using RenderMan-compliant render engines. We strongly recommend the Aqsis (http://www.aqsis.org) render engine for use with K-3D.

K-3D's innovative [censored] tutorial system will introduce you to basic use of the program. New tutorials can easily be recorded and shared with the rest of the community.

K-3D allows you to create and edit documents in multiple realtime OpenGL solid, shaded, texture-mapped views. You can even model, animate, and interact with animations while they play back for maximum productivity!

No support for Poser at the moment, but because K-3D system supports Python...