I'd love to see these two projects merged together: https://rubyapi.org/ and https://basesecrete.github.io/rorvswild-theme-rdoc/
I couldn't find a way to force the table of contents drawer out from the right side of the screen when the screen is too narrow to show it by default, but otherwise it looks pretty good to me?
And it is important, isn't it? Not everyone has a second monitor attached all the time, sometimes you do want to look things up on your phone.