darktable is an open source photography workflow application and raw developer:
https://www.darktable.org/
0:00 Intro
0:55 edit 1: White balance with color channel modes
7:20 edit 2: White balance with color channel modes and multiply
17:58 edit 3: multiply and divide with color calibration module
22:59 edit 4: multiply with color calibration module
24:39 edit 5: divide in darktable and in GIMP
27:42 edit 6: subtract with diffuse and sharpen
28:58 edit 7: difference blend mode in GIMP
30:57 edit 9: geometric and harmonic mean
33:32 edit 10: color grading with color channel modes
35:18 edit 11: lightness and chromaticity
Free/Open Source Photography:
https://pixls.us/