Has anyone been successful in using any of the Fab 40 templates in a SharePoint 2013 Foundation environment?
SharePoint 2013 has much better support for 2010 solutions than 2010 did for 2007. Most SharePoint 2010 solutions will deploy to SharePoint 2013 and work just fine (some may require your site collection to run in 2010 mode). It doesn't appear that anyone (at least not publicly online) has done much testing with the Fab 40 templates on 2013 specifically. With that said, however, if you use the guides and solutions for installing them on 2010, you should have nearly the same success rate that people had running them on 2010.