What are some alternatives?
When comparing Indigo Renderer and Keyshot, you can also consider the following products
appleseed - appleseed is an open source, physically-based global illumination rendering engine primarily designed for animation and visual effects.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Mitsuba - Mitsuba is a research-oriented rendering system in the style of PBRT, from which it derives much inspiration.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
RenderMan - Advanced Technology from Pixar Animation Studios for Rendering VFX and Animation
V-Ray - Learn why V-Ray for 3ds Max’s powerful CPU & GPU renderer is the industry standard for artists & designers in architecture, games, VFX, VR, and more.