It is possible to customize the shortcuts, though it's a bit cumbersome. In Settings under the Hotkeys tab, you can download a JSON file describing your mappings, edit it, then re-upload it.

Looks a lot like https://gingkoapp.com/ . Any connection?

Is this a better or open-source alternative to it?

Gingkoapp is general(academic papers, gtd, etc), Nulis is focused on fiction writing.

I write stories and screenplays, and while gingko is awesome, I need many features it doesn't have(editing all the cards at once like a big text document, writing stats and word targets, good fullscreen editor, custom templates, fountain markup, color coded cards, collapsing branches, outline-view, saving files locally, a desktop version, a bunch of other things).

Nulis is in it's very-very early version, I've just barely deployed it, but I do think that it's going to be much better for writing fiction.

I would really love to open source it, but for now having a viable business model is a must, I need it so I could afford to make Nulis as good as I want it to be. If I figure out how to make it work despite being open source, or develop it to the point where it benefits more from being open source than not, I'll gladly do that.

It's possible that I will set up a patreon, and open source it once it reaches enough donations to become sustainable.

Gingko is really amazing and very refined. Highly recommended -- one of a handful of tools that have changed how I work.