Blender

Blender is a generalist free 3d software that aims to provide a comprehensive, end-to-end 3d content pipeline that can produce 3d feature films all on its own. To that end it includes many features that the other main packages like 3ds Max and Maya might opt to leave out, such as camera tracking, compositing, multiresolution sculpting, texture painting, etc. However, there is no obligation to use a particular feature of Blender if you don't need it or if it's not quite production-ready, and Blender shines the most when you customize it for your particular specialized workflow.

Users who are coming to Blender after using 3ds Max should read the 3ds Max to Blender migration guide. Users who are coming to Blender from Maya should read the Maya to Blender migration guide. Everyone should read the Blender customization guide for some useful addons and saner defaults.