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).
Arion is the hybrid-accelerated and physically-based light simulator developed by RandomControl. It inherits all our expertise in light simulation and makes it run on steroids, thanks to our very unique approach to massive CPU+GPU+LAN computation.
mental ray® is a rendering software which generates images of outstanding quality and unsurpassed realism. The software combines the physically correct simulation of the behavior of light with full programmability for the creation of any imaginable visual effect.