dangle writes "F.A.T. Lab and Sy-Lab have officially released their Free Universal Construction Kit, allowing builders to freely interconnect parts from Lego, K'Nex, Fischertechnik, and other common building sets. ZomeTool and Zoob patterns will be available after related patents expire. The makers have also spent considerable effort investigating and anticipating legal complaints from manufacturers, using an Inverse Think of The Children Argument: Some may express concern that the Free Universal Construction Kit infringes such corporate prerogatives as copyright, design right, trade dress, trademarks or patents of the supported toy systems. We encourage those eager to enforce these rights to please think of the children — and we assert that the home printing of the Free Universal Construction Kit constitutes protected fair use." Model files are available over at Thingiverse. The designs are all covered by the CC BY-SA 3.0.