I don't, but I do use, and am interested in, their software. So it's a bit disappointing to see a link to their site while using hn on mobile, only to get to a page that's isn't that doesn't display anything useful.

But the components are not supposed to work on mobile so what is there to see?

You seem to assume that everybody on this website knows what Ring UI is. But I didn't know and judging from quite a few other comments here, I wasn't the only one. All we had to go by was the title "JetBrains Ring UI" and a comment stating that a date picker looks nice. Without any kind of description it's not that weird to assume a website with a datepicker works decently on mobile.

I wouldn't be investing effort improving the mobile browser behavior of desktop oriented controls for the benefit of making it a better HN submission.

I think you've missed the point of the previous comment.

So, these are components for building their IDEs? They can't be used for anything else?

JetBrains has web applications which is where these are used - YouTrack, Space, TeamCity.

I'd totally use them on my mobile devices if versions for them existed. They're just too convenient even though they lack a keyboard. Wish I could use them to write software.