There's a new calculator for OAS and GIS at

It's not complete as it wimps out if you don't have a full OAS pension (less than 40 year residency in Canada), but it works well if you do.

I'm excited about it because it's the first time I see any source code (the javascript is right there in the html source of the page) for calculations available for any calculations from the Canadian government. The US social security system has provided full source code for their calculations for many years.