Deeds. Mortgages. Liens. Fun stuff.
ETA: For whatever reason, I could rarely find details about existing homes being offered for sale on RealtyTrac, so I have cancelled out of that. I think if I were specifically looking for a foreclosure sale, that might have continued to be useful, altho I think if I did that again I'd dig a little harder on what the Warren Group has to offer. But the Massachusetts Registry of Deeds is free and comprehensive. Yum.