LuxCoreRender/BlendLuxCore

This hardware-agnostic rendering plug-in for Blender uses accurate ray-tracing technology to produce images and animations of your scenes, and provides real-time interactive rendering and continuous adjustment of effects.

LuxCore source repository

The Cycles Render Engine - official mirror

3D Engine with Blender Integration

Simple Open-source Ray Tracer

MoonRay is an open-source, award-winning, state-of-the-art production path tracing renderer, initially developed at DreamWorks and an active member project of the Academy Software Foundation.

Custom build of blender with some extra NPR features.

Embeddable physically based renderer

c-ray is a small, simple path tracer written in C