I know this isn't explicitly on topic, but that logo is a non-starter for me. You could have the most interesting article in the world on that page and that character in the top left corner is going to instantly cut your page views.

I think the slow factor you were experiencing had more to do with the tablet. Front-end engineers use tools like jsFiddle and Plunker constantly, they are especially useful for demonstrating componentized code. Here's an example of a currencyFormat tester I made to speed up the dev cycle with my Testing/PM team on a project. By sending them this link, they were able to get instant feedback about what the function did and then let me know what customizations they wanted. (For instance, they wanted percents to be preserved.)

Don't forget about Plunker which allows you to sign in directly with your GitHub account and use linked files.

I use these tools constantly, but I don't think they satisfy OP's requirement of large scale projects. I've never known anyone to use an online IDE for a large-scale project, but I think if the correct tool were developed I would be interested in trying it.