Modio is a cool app that is basically a library of home 3D print ready parts for robots that you pick from to assemble in software, then download to your computer for slicing and printing. It exports to STLs so it can work for any 3D printer. I played with it a little when it first came out on a borrowed iPad, but since I don't have an iDevice myself that initial playing with was all I had until recent. I discovered they have an android in beta that I asked to get into.
Let me just say that this isn't beta in my mind. It's complete. The download function is super clever. The library is robust and the customizations add an additional layer of possibility. My kids love playing with it.
So 3 of my kids are getting their own custom created robots this Christmas with interchangeable parts. If that's not cool, I don't know what is.
Some of the parts are pretty challenging to print and require a well tuned machine. But that's what you get with impressive models.