I've used Graphviz for many years and my main gripe with it is the lack of customization. Yes, there's "some" customization, but there's a point (not too far from the initial style) where, if you don't like the output, you're out of luck and might as well redraw it using draw.io or some other WYSIWYG editor.
Graph viz is admirably powerful, even here. The main techniques seem to be invisible objects and custom code, in case that helps. The cassowary solver group in Australia (I'm blanking on the university, Monash?) goes further via custom constraint logic, and I believe iOS layouts were deeply inspired, and maybe even had one of their students.
Graph technologies are tricky to build up -- you can go deep in many areas like this. Afaict, AT&T/Bell Research used to be the main developers of graphviz, and when that corporate lab thinned out, so did graph viz development. A similar story happened with gephi devs when they left their universities (was popular in social data), and cytoscape (popular in bio) is still largely at that fragile state.
We are historically big contributors to OSS at Graphistry, but saw the history of funding issues in this space, and how each tool reached a frustratingly low ceiling due to it. We decided to not start as open core, and instead made a free GPU tier + release individual pieces as OSS (Apache Arrow's JS tier, etc) + initially charge for GPU code, until we could build + grow more commercially targeted parts. Thankfully, we are getting to the point of enough sustainable revenue that we are pushing much more to our OSS libs now, and one of our OSS pushes for 2022 will be moving custom (GPU-accelerated) traditional layouts & AI layouts to the OSS lib pygraphistry :) A request we get often get for pygraphistry and our file uploader UI is dotfile (and graphml/gexf) conversion/ingest for then viewing+editing in our scalable interactive graph renderer, so we have been thinking of adding a pygraphistry example just to demonstrate the OSS flow!
