Because Nulis is written in React, frontend and backend are pretty much separate. Mongo/Node just create an api and send/receive trees formatted as one big json object. Backend is very simple, and should be easy to replace with anything else.
Also, you can just use file>save/open feature, which saves a tree as a json file, purely from the frontend.
The desktop version of the app can work without the backend at all(server used just for cloud sync, all trees are saved as files).
Note that Desktop is in a very early version, Mac/Windows are not tested at all. I'll keep updating it and making it more stable as I continue the development.
Also, you can just use file>save/open feature, which saves a tree as a json file, purely from the frontend.
The desktop version of the app can work without the backend at all(server used just for cloud sync, all trees are saved as files).