Swidget works on Windows or Mac OS, but only supports Firefox on the Mac. On Windows, Chrome, Internet Explorer and Firefox are all supported. Once installed, the add-on places a button at the top of banner and block ads to click that replaces them with a widget that you choose.
The gallery of widgets is broad: you can choose weather, stocks, clocks, headlines and more. The only downside is that Swidget doesn't work automatically: you have to click to replace each ad on the page one at a time.