Picogen is described as 'A free Terrain Synthesizer and RendererPicogen is an outdoor ray tracing system, a free Terrain Synthesizer and Renderer targeting large-scale terrain with realistic day/night-illumination and detailed plant populations'. There are more than 25 alternatives to Picogen for a variety of platforms, including Windows, Mac, Linux, LightWave and Autodesk 3ds Max. The best alternative is Terragen, which is free. Other great apps like Picogen are Adobe Dimension (Paid), LuxCoreRender (Free, Open Source), Vue (Paid) and POV-Ray (Free, Open Source).
Adobe Dimension (formerly Project Felix and then Adobe Dimension CC) is the 3D design tool made for graphic designers. With extensive integration with Adobe Stock, you can easily composite 2D and 3D assets to build product shots, scene visualizations, and abstract art.
LuxCoreRender is a physically based and unbiased rendering engine. Based on state of the art algorithms, LuxCoreRender simulates the flow of light according to physical equations, thus producing realistic images of photographic quality.
The Persistence of Vision Raytracer is a high-quality, totally free tool for creating stunning three-dimensional graphics. It is available in official versions for Windows, Mac OS/Mac OS X and i86 Linux. The source code is available for those wanting to do their own ports.
appleseed is a modern, open source, physically-based rendering engine designed to produce photorealistic images, animations and visual effects. It provides individuals and small studios with an efficient, reliable suite of tools built on robust foundations and open technologies.
PhotoRealistic RenderMan, or PRMan for short, is a proprietary photorealistic RenderMan-compliant renderer. It primarily uses the REYES algorithm but is also fully capable of doing ray tracing and global illumination.
NOX Renderer is a rendering software based on unbiased methods. The renderer is available as a standalone Windows executable with a plug-in to link it to 3ds Max. A linking script is also available for Blender users.