Roblox - Reimagining the way people come together.
Shapeways - Shapeways - 3D Printing Service and Marketplace
Lunacraft - Lunacraft focuses on Endless Creativity and Exploration elements.
3D Hubs - Airbnb for 3D printing
Blockland - Blockland is a non-competitive multiplayer sandbox-style construction game. It's kind of like playing with legos on the internet.
i.materialise - i.materialise is an online 3D printing service, community and marketplace.