[donatzsky]

There are actually a number of more-or-less node/graph-based image editors:

# chaiNNer

Fully node-based image processing.

https://github.com/chaiNNer-org/chaiNNer

# vkdt

Node-based raw and video editor. Sort of the evolution of darktable, by the original developer.

https://jo.dreggn.org/vkdt/readme.html

# darktable

The graph is strictly linear (single input, single output), but you can change the order of the processing and insert new nodes as you want.

https://www.darktable.org

Pretty sure there are some others, but those are the three I can remember right now.

[dleeftink]

Oldie but goodie is Nodebox[0] and for data-driven/dynamic compositing see Cables.gl[1]. Kirell Benzi's work uses the latter and is nothing short of breathtaking[2].

[0]: https://www.nodebox.net/

[1]: https://cables.gl/

[2]: https://youtu.be/CltYdTVH7_A

[Zecc]

Natron is also pretty well-known, I think?

https://natrongithub.github.io/

[CyberDildonics]

Are you asking if it's well known? I don't think it is actually used in any context, it is so unstable that if you start it and do nothing, it will crash in a few seconds.