Does anyone know of a small, limited functionality lightbox built with pure javascript? This is for an embeddable widget, thus the reason of not using jquery. All I really need is creating an overlay for a specific div or simply by passing some HTML.
There's a great list/comparison of lightboxes here. You can quickly scan which require a JS library (jQuery, MooTools, etc.) and which don't, and you can also see what features each supports. There's a sizable chunk of them that don't use any JS library, so you should be able to easily find one to suit your needs.
Here's a few to get you started: