Cycles is Blender’s physically-based production renderer.
To use Cycles, set it as the active render engine in the Info editor’s header. Interactive rendering can be started by setting a 3D View editor to draw mode Rendered using Shift-Z. To perform a full render go to Properties ‣ Render here you can either choose to render a still image or an Animation.
Cycles may be able to use your GPU for faster rendering. To see if and how you can use your GPU for rendering, see the documentation on GPU Rendering.
The source code is available under the Apache License v2, and can be integrated in open source and commercial software. Cycles is natively integrated in Blender, Poser, and Rhino.