As far as I understand, "the hard part" of a web browser is not the front end but the rendering engine. I imagine that's where most of the current code is.

Hey! I’m one of the creators of Beaker. Beaker is built with Electron, a wrapper around Chromium, and it doesn’t include any UI elements like tabs or the URL bar. We made those ourselves, and have taken inspiration from a number of browsers.

What you see here is actually the “old” version of Beaker - a lot has changed in the upcoming release. Here are a few tweets with screenshots if you want to see a preview:

https://twitter.com/taravancil/status/906583737789542400

https://twitter.com/pfrazee/status/910988429881675782

https://twitter.com/taravancil/status/918232881641779201