Sourcegraph is the closest external thing I've found to Google's internal web tool for viewing code.

The startup I'm at (ersc.io) is working in this space (version control more than the IDE side of things), because, in my opinion, there just plain isn't any.

https://github.com/jhuangtw/xg2xg has a broader list

The only thing remotely close is a monorepo checkout ... with all the problems that come with that.