Blender is a free and opensource 3D object modeling applications works in cross-platforms. Blender 2.58 stable version has been released and available to install In Ubuntu 11.04 Natty Narwhal and older versions using PPA.
Check Blender features and more information Here.
Install Blender 2.58 Stable In Ubuntu 11.04 Natty Narwhal
sudo apt-add-repository ppa:cheleb/blender-svn/ubuntu
sudo apt-get update
sudo apt-get install blender
[note] PPA works in Ubuntu 11.10 Oneiric, Ubuntu 10.10 Maverick, Ubuntu 10.04 Lucid, and Ubuntu 9.10 Karmic[/note]