@avrionov @ignoramous Thank you!

The frontend for desktop/browser React, and Electron is used to create standalone apps. I don't love Electron, and if you don't want it a browser version is available too: https://app.actualbudget.com/

The mobile app uses React Native and has a custom UI just for mobile, but it shares styles and a few small components with web. I don't believe that you can build one UI that works well on both desktop and mobile.

All platforms share the backend code which runs in a separate process/thread. On mobile, I use https://github.com/JaneaSystems/nodejs-mobile to run the JS backend locally.

That's mostly it. No UI frameworks are used. I love UI/UX design so I built it from the ground up to be as usable and performant as possible.