To celebrate 15 years of G'MIC development, here's their project progress report, summarizing 1½ year's work.

Reported to work on "Affinity Photo" as well.

I second that. G'MIC has an impressive bunch of built-in commands to manipulate images, see e.g. the examples shown in the reference documentation (click the first magnifying glass, then use right arrow on the keyboard):

http://gmic.eu/reference.shtml#subsection15

And as the commands are built-in, no needs for external scripts, those effects are available from any interface using the `libgmic` API (including C/C++ programs).

Awesome!

It is announced as an "image processing tool". This is a field mostly interested in raster images usually.

G'MIC home page is : http://gmic.eu

It's a very popular plug-in for GIMP. I don't think this is an alternative to ImageMagick

I marked it as alternative only because it has full command line support, which is rare case for filters. But it is mainly strong filter library, than batch convertor/resizer, you are right.