This: basically another Sketch. Currently the only "modern tool" that works cross platform is Figma.

I've been enjoying using Figma. I definitely wouldn't mind a non-Electron based app of it.

Of Figma? There is the web version of it which is the same as the desktop app. Or did I misunderstand?

Somehow I’ve missed they had desktop versions. I thought it was web only.

The desktop version of Figma is built using Electron. The web version is not.

How does one build the web version of something using Electron? ;)

I was trying to make that point without the snark :)

Well, you've also got Affinity Designer, which is quite good if you prefer a desktop app with no subscription fees (i.e. proper dekstop app and not an electron app).

Also Adobe XD. I know people give Adobe crap for coming to the party late, but the new tool is quite good with prototyping and web sharing built in, plus they launched freemium model. Framer is great for more advanced prototyping needs w/ animations/transitions/etc, but the XD is pretty good and fast for many needs, and it's Mac + PC.

There is the web-based Gravit Designer:

https://www.designer.io/

Somehow that page manages to be just as infuriating as the one for framer. Why do I have to wait for elements to be blended in so I can read them... They should at least make them keep being displayed once they were shown.

Windows version is in the works. You can sign up to be notified.

https://framer.com/forms/windows/