I think the point is, the title "Mail.app implemented on the web using ukijs" is wrong. It's pretty easy to clone a UI so something looks like something else.

I think the point is, the title "Mail.app implemented on the web using ukijs" is wrong. It's pretty easy to clone a UI so something looks like something else. It's easy enough to then add a bit of data so it sort of feels like it as well. But building a real world fully functioning app takes a bit more work.