I have been working with Visual Studio online, and the capabilities are absolutely stunning for a browser-based solution.
I have been through a period where I had to switch computer frequently, and as a result was looking for a online IDE. With everything in the cloud, I wouldn't need to spend lots of time reconfiguring my work environment each time I start working on a new machine.
My IDE of choice has been the excellent Jetbrain PHPStorm since more than a decade, so I was looking around for cloud offerings that mimic that. Those weren't easy to find.
I did stumble by chance on a link on github that proposed me to open a repository in Visual Studio online. Just out of curiosity I had a look and I remain absolutely impressed up until today. Microsoft has managed to build a version of its open source IDE inside a browser, with effortless Github connectivity and even support for a limited set of plugins.