I've been touting Darktable as an option recently, since they added their 'negadoctor' plugin.

So first, https://www.darktable.org/ is an open source package that started as an alternative to Lightroom. It's really designed for RAW development, batch processing, organization, culling, proofing, etc.. It's more Lightroom than Photoshop. It's also "non-destructive"-- all of your edits, adjustments, crops, rotates, etc., are stored in metadata files, rather than changing your source image. This also makes it easy to apply those edits to other photos.

It's available for Windows, Mac OS and Linux-- while it's part of most linux distributions, be aware you need at least version 3.1 (3.2 is better) for the negadoctor plugin, and many distributions lag behind the latest and greatest by a few months.

negadoctor seeks to fill the same role as Negative Lab Pro-- invert and correct for color cast. Automatic works pretty well, but you can also tweak in semi-automatic or full manual mode.

This video (and following videos) does a nice job introducing Darktable:


And this one covers negadoctor: