Sunflow Rendering System is described as 'Sunflow is an open source rendering system for photo-realistic image synthesis. It is written in Java and built around a flexible ray tracing core and an extensible object-oriented design'. There are more than 25 alternatives to Sunflow Rendering System for a variety of platforms, including Windows, Mac, Linux, Autodesk 3ds Max and Sketchup. The best alternative is Adobe Dimension. It's not free, so if you're looking for a free alternative, you could try Cycles Renderer or LuxCoreRender. Other great apps like Sunflow Rendering System are POV-Ray (Free, Open Source), Keyshot (Paid), V-Ray (Paid) and appleseed (Free, Open Source).
Clara.io is a full-featured cloud-based 3D modeling, animation and rendering software tool that runs in your web browser. With Clara.io you can make complex 3D models, create beautiful photorealistic renderings, and share them without installing any software programs.
Pixie is an open source RenderMan renderer for generating photorealistic images. You can compile Pixie on Windows (using Visual Studio 2005), Linux and on OSX (using XCode or unix style configure script).
Thea Render is a state-of-the-art biased/unbiased renderer with a rich set of innovative features, a powerful material system and its own advanced studio, all-in-one. Plugins are available for 3dsMax, Blender, Cinema4D, Rhino, SketchUp and SoftImage.
YafaRay is a free open-source montecarlo raytracing engine released under the LGPL 2.1 license. Raytracing is a rendering technique for generating realistic images by tracing the path of light through a 3D scene.