LightZone - A Very Capable Free Tool
I want to draw your attention to LightZone - http://lightzoneproject.org a very capable image editing tool with some very unique capabilities. I had purchased LZ in the ver 1.0 days when it was a commercial product. Eventually, the creator of the product open-sourced the code and it is now free. What initially attracted me to LZ was it's ability to let you edit in Zones (Zone System), resulting in a very powerful way to manipulate tonal distributions and very powerful for B&W. Also terrific for color. Totally non destructive workflow - original RAW files are not touched. 16-bit linear color space for an extremely large gamut, powerful RAW profiling allows users to create custom profiles, terrific selection and masking. Tone-mapping for single-image extended dynamic range images. Great B&W conversions.
There are a ton of videos showing how it works here - https://www.youtube.com/channel/UCGob3KtUcRJqz-GwA5Owbdg
It's a worthy tool to have in your image processing toolbox. Check it out!