Something that when the rest of someone's computer is slowing down, this can stay responsive.
Not everyone has the fastest hardware or much ram; people like to have 100s of tabs open; and CPU's overheat and throttle, especially laptops.
However it relies on two important things:
1. Using something which uses the OS's built in browser (rather than something like Electron).
2. Keeping your JS very lightweight.
This was shared a few days ago, combined with py2app could be a winner:
Yeah so without having to overwrite some very deep OS settings, which will likely raise some red flags for your app requiring administrator privilege to run, you aren't going to get this. If someone has a browser thats taking up most resources, its gonna throttle everything.
There is generally very little reason to write anything but web apps these days for things that don't need to touch specific hardware. If you stick to as much native js/css/html as possible (i.e avoid large libraries), it will load blazingly fast and use way less resources then web apps that are considered fast.
You're not going to hit your responsiveness goals otherwise. And it's not going to feel native otherwise (if anyone actually cares about that anymore, I dunno)