Blender comes with a powerful unbiased rendering engine that offers stunning ultra-realistic rendering.
Cycles is Blender’s ray-trace based production render engine.
FreeStyle is an edge- and line-based non-photorealistic (NPR) rendering engine. It relies on mesh data and z-depth information to draw lines on selected edge types. Various line styles can be added to produce artistic (“hand drawn”, “painted”, etc.) or technical (hard line) looks.