It is — well, not entirely, but it can be — a context menu, triggered by a click & hold gesture with your left (or at least primary) mouse button, written in JavaScript. It is an otherwise non-functional proof of concept.
Why click & hold and not just a right click?
Because right clicks are usually already reserved for the browser's context menu. Personally, I find it most annoying when a site disables it/uses it for its own purpose. However, contextual menus themselves can indeed be pretty useful.
Cool! So how did you pull it off?
Simply put, it just sits there waiting for you to click & hold your primary mouse button. When you do, it creates the menu and displays it wherever the pointer was when you first depressed the button (ideally still at the same spot). For the complicated answer, I'll just let the JavaScript speak for itself.
Can it be bound to a specific element instead of document?
Sure, event handlers can be attached to any DOM element. I chose document for this demo because it conveniently covers the entire viewport.
Can it be used for [insert desired behavior] instead of context menus?
Why not? Simply make your event handler do [insert desired behavior].
Can this be made into a plugin for [insert favorite library]?
I made a jQuery plugin that adds the click & hold gesture as a custom event. I imagine this can be turned into a plugin for other libraries as well.
Why the !@#$%^& is this stuff all fancied up with CSS3?