[mikkqu]

Maybe not the best place to ask, but is it known what engine is used behind his website?

I can assume it's probably something custom made? I like the way topics are structured, the navigation is clear, nice comment section.

Are there any known tools or service capable of building a full-featured website like this? Any good open source projects? (please no jokes about Wordpress)

[gitgud]

Yes, it looks like a Zurb site? (what ever that is) https://foundation.zurb.com/

If you're interested in the tech behind websites, then I recommend getting the Wappalyzer extension for your browser, It tells you what software is most-likely running on a specific website you're looking at.

[aptwebapps]

Zurb Foundation is the inspiration for Bootstrap (some people would say it's a bit more than just the inspiration).

[vicpara]

or find out yourself here: https://builtwith.com/?https%3a%2f%2fwww.gatesnotes.com%2f

[zipperhead]

I don't know but it seems to break Vimium-FF navigation. None of the keyboard mappings work.

[pacuna]

Probably something custom made with .NET Framework. Try the builtlwith extension.

[sfotm]

You could do something like this with Jekyll, which is supported on GitHub pages. You'd need to put some work into it to get the same features Gatesnotes has, but the framework is there.