I've used the Nitrous.io editor before. They provide an online development environment for Node.js, Rails, and a few other things. Their editor is great for quick edits, but I think the lack of extensibility in all the online editors/IDEs I've tried means they're basically a no go.
This jQuery plugins will track scroll progress through targeted elements. When a targeted element is scrolled to, a fixed progress bar will appear at the top of the window to show progress through the element.
I whipped this up quickly after seeing examples of a few sites with this feature. I wanted to make a plugin so I could easily add this to a site. If you have any ideas, or notice any issues, please post them here or on Github and I'll do my best to address them.
I'm also spoiled by Sublime Text.