Looks like @Sidane may be the user who runs/works on that website you linked to (the website is linked to on his profile). He may be worth contacting.
Also the add-on appears to have references to EWRblock_TabbedContent.css in the code - this is likely from the XenPorta add-on, the author of that add-on is @Jaxel he may be able to provide some insight as to how that is achieved.
You could probably accomplish something very similar with [bd] Widget Framework using Widget Groups (they create the tabs, and have different widgets on each one. At that point it's just a matter of changing up some CSS