You can download Renderman for free from the Pixar Renderman website, and it can be used for any project that doesn't generate commercial profits.
Renderman is best know for producing Pixar's CG animated films such as Monsters University (above), but is suitable for both animation (such as the The Lego Movie, below top) and VFX work (such as Godzilla, below bottom).
Renderman 19 - both the free and commercial versions - ships with plugins for Maya (2013.5, 2014 and 2015 and The Foundry's Katana (1.5, 1.6 and 2.0). Pixar is currently working on plugins for Cinema 4D and Houdini, and it's 'potentially' working on plugins for 3ds Max, Modo, Rhino, Lightwave and Blender.
This new version debuts Pixar's RIS technology for global illumination and interactive shading and lighting for artists, which will first be used in one of Pixar's own productions in the forthcoming Finding Nemo sequel, Finding Dori. Renderman runs under Linux, Mac OS X and Windows.
Download Renderman for free
You can download the non-commercial, free version of Renderman here.
See what the latest version of Renderman is capable of in the film below.