An open source building toy is printable and modifiable by anyone interested in using the toy. One such toy system is the Kickstarter funded TIN TOY project. https://www.kickstarter.com/projects/804215203/developing-a-21st-century-open-source-building-toy
We will have a collection of TIN TOY parts for you to experiment and play with. We will also be seeking your feedback about how the building toy can be improved!
As 3D printers become less expensive and faster we hope to have a great open source building toy ready and available for anyone to download, print, use and modify for their own particular interests.
If you would like to get started the files for TIN TOY are available on Thingiverse here: http://www.thingiverse.com/thing:166730