[pixelpoet]

There's also Indigo Renderer and the open source LuxRender:

https://indigorenderer.com

https://luxcorerender.org

[dagmx]

Note that Lux isn’t spectral anymore. The older version is though.

[pixelpoet]

Funny, I added the original implementation of spectral rendering to Lux and then they took it out :D

[nextaccountic]

Why did they remove it?

[pixelpoet]

I have no idea (it wasn't exactly the same project, LuxCore vs Lux), and PBRT, on which Lux was based, later moved to full spectral rendering.

I guess they feel they'd rather reduce register pressure a bit than support it.