The F.A.T. Lab and Sy-Lab hackerspaces have combined forces to develop the Free Universal Construction Kit (don't worry, they drop "Free" for the acronym: UCK). The kit consists of 3D printer design files for 80 adapters that provide interconnections and interoperability between ten popular children's construction toys including Lego, Duplo, K'Nex, Lincoln Logs, Tinkertoys, Zome, and other less well known kits. They even have one adapter brick that has all ten connectors on it! All of the part designs are released under the Creative Commons BY-NC-SA license. Lots of robot builders use one or more of these construction kits, so I expect these will be a boon to roboticists. The group has anticipated negative reaction from the corporations who control the "intellectual property" (doing the right thing is seldom profitable). So the groups also see this project as a "transgressive architecture" that promotes civic activity.
Most market leaders regard interoperability as an anti-competitive nuisance, a regulatory check on their ambition, or a concession to the whining of lesser players. Quite simply, interoperability is the request of the disenfranchised. And which end-user, in so many ways, is less enfranchised than a preliterate child?
You can download individual adapters from Thingiverse.com. The entire kit of designs is expected to be available via bittorrent from The Pirate Bay's physibles channel soon (which should protect it from any legal threats). Hit the 'read more' link to see videos explaining the problem and UCK as the solution.