In mid-2014 Pixar announced that it would release the RenderMan (own rendering engine used in the company's animations and in many Hollywood films). After a short delay, behold, it is now available to everyone!
The simple rule: everyone can use the software as long as it is not for commercial purposes. The cool thing is that the fully functional version (that is, without a watermark or any other limitation that we are used to seeing in the market) the company posted a FAQ (frequently asked questions, or frequently asked questions) taking away many of the doubts that may arise.
As reported by the Ars Technica, Pixar requires that you create an account on the official RenderMan forum and provide a valid email address. Once this is done, you receive an installation package that downloads everything you need to run the software (either for OS X, Windows or Linux).
It is worth noting that we are talking about the animation rendering engine. No one will download RenderMan and go out and create animations. For that, you also need to have 3D animation / modeling software like Maya (from Autodesk) or Katana (from The Foundry). Support for Cinema4D, Houdini, 3DS Max, Modo, Rhino and Lightwave software are on the way; for Blender and Nuke, there is no forecast.