Blender

Blender is a free open source  3D graphics  application, available under the GNU general public license  for the Linux, MAC OS X, FreeBSD , OpenBSD and Microsoft Windows  operating systems.

Features - 

Interface -

• Non-overlapping and non-blocking UI delivers unsurpassed workflow
• Flexible and fully configurable window layout with as many screen setups as you prefer
• Undo support on all levels
• Anti-aliased fonts with international translation support
• Any window space can be easily switched to any window type (curve editor, NLA, 3D view etc)
  
• Built-in text editor for annotations and editing Python scripts
• Graphical user interface for Python scripts
• Fully scriptable UI with custom themes
• Consistent interface across all platforms

Modeling-

• A range of 3D object types including polygon meshes, NURBS surfaces, bezier and B-spline curves, metaballs, vector fonts (TrueType, PostScript, OpenType)
• Very fast Catmull-Clark subdivision surfaces with optimal iso-lines display and sharpness editing
• Full multiresolution sculpting capabilities with 2D bitmap/3D procedural brushes (Paint, Smooth, Pinch, Inflate, Grab) supporting symmetry
• Modifier stack deformers such as Lattice, Curve, Armature or Displace
• Mirror modifier with middle vertices clipping and automatic deletion of inner faces
• Non destructive real time Boolean and Array modifiers
• Mesh modeling based on vertex, edge and/or face selection
• Smooth soft selection editing tools for organic modeling
• Python scripting access for custom tools

 Rigging-

• Fast skeleton creation mode
• Interactive 3D paint for vertex weighting
• Fast envelope based skinning
• Automatic Skinning that really works (heat equilibrium based)
• Mirror editing (bone creation and weight painting)
• Double Quaternion deformation reduces shrinking and other bone deformation errors
• Volume deformer uses a mesh cage to deform complex meshes with great results
• Bone layers and colored groups for better rig organization
• B-spline interpolated bones; forget about elbow twists
• Constraint stack for IK solver setup and other constraints
• PyConstraints; if you need something not yet implemented code it in python with real time feed back, no compiling needed

Rendring-

• Fast inbuilt raytracer
• Oversampling, motion blur, post-production effects, fields, non-square pixels
• Tile-based and fully threaded
• Render layers and passes
• Render baking to UV maps and object to object baking (full render, ambient occlusion, normals, textures)
• Render engine tightly integrated with the node compositor
• Halo, lens flares and fog effects
• Vector motion-blur post-process effect (using node compositor)
• Realistic defocus (DOF) post-process effect (using node compositor)
• Edge rendering for toon shading
• Interactive preview rendering panel in any 3d view
• Ambient Occlusion
• Approximate Global Illumunination
• Export scripts available for external renderers such as Renderman, Povray, Virtualight, Lux, Indigo and V-Ray - See Resources for a full list.

Animation-

• Armature (skeleton) deformation with forward/inverse kinematics with pole target support
• Auto IK allows posing FK chains easily
• Non-linear animation editor for mixing individual actions created in Action editor
• Automated walkcycles along paths
• Animated constraint system
• Vertex key framing for morphing, with controlling sliders
• Edit and create new blendshapes from existing targets
• Character animation pose editor
• 'Ipo' system integrates both motion curve and traditional key-frame editing
• Audio playback, mixing and editing support for sound synchronisation
• Timeline offers fast acces to many playback functions, autokey, help markers
• Python scripting access for custom and procedural animation effects

Shading-

• Diffuse shaders such as Lambert, Minnaert, Toon, Oren-Nayar, Lambert
• Specular shaders such as WardIso, Toon, Blinn, Phong, CookTorr
• Node editor for creating and mixing complex materials
• PyNodes: write your own Python shaders with realtime feedback, no need to compile
• Material previews rendered by main render engine
• Fast, realistic subsurface scattering
• Blurry reflections and refractions
• Tangent shading to give any shader an anisotropic effect
• Versatile procedural textures system
• Reflection maps
• Normal, displacement and bump maps

Realtime 3D/ Game creation -

• Graphical logic editor for defining interactive behavior without programming
• Collision detection and dynamics simulation now support Bullet Physics Library. Bullet is an open source collision detection and rigid body dynamics library developed for Play Station 3
• Shape types: Convex polyhedron, box, sphere, cone, cylinder, capsule, compound, and static triangle mesh with auto deactivation mode
• Discrete collision detection for RigidBody simulation
• Support for in-game activation of dynamic constraints
• Full support for vehicle dynamics, including spring reactions, stiffness, damping, tyre friction etc
• Python scripting API for sophisticated control and AI, fully defined advanced game logic
• Support all OpenGL^TM lighting modes, including transparencies, Animated and reflection-mapped textures
• Support for multimaterials, multitexture and texture blending modes, per-pixel lighting, dynamic lighting, mapping modes, GLSL vertexPaint texture blending, toon shading, animated materials, support for Normal Maping and Parallax Mapping
• Playback of games and interactive 3D content without compiling or preprocessing
• Audio, using the SDL toolkit
• Multi-layering of Scenes for overlay interfaces