Blender
From Game Making Tools Wiki
Blender is mostly recognised as a free 3-D modeller (with an idiosyncratic interface), but it also functions as a game maker and video editor.
Bforartists
Bforartists is a fork of Blender aimed at remedying Blender's often complained about interface, making it more intuitive. It's probably not quite ready to use at, but worth keeping an eye on!
Blender and Unity 3D
Blender and Unity treat models a little differently: The forward direction is X in Blender and Z in Unity >:[ [post helpful stuff re this here~]