TL;DR: Golan Levin designed printable pieces which can be used to connect previously incompatible toy types together (LEGO, Playmobil, DUPLO, etc).
As a consequence, this raised a myriad of copyright infringement questions for the future of 3D printable content.
But see the problems Thingiverse have had, having to deal with DMCA takedown notices. (Luckily the person dropped the DMCA takedown case.)