Cement is massively energy-hungry in its manufacture. And it also uses a lot of energy in transporting it from the factory to your building site. So here's a business, called Origami 4, that lets you order just the essential chemicals online, while you supply the bulky sand and materials that are costly to transport.
This is not just a case of buying a bag of cement and mixing with sand and stone as you might do normally to make concrete. You are actually mixing the cement itself in a special machine, BEFORE even making the concrete, and packing it in bags like the ones you would buy at the hardware store. So the transport saving is significant if you make a lot, and have sand available nearby. And if you use this method, you're going to want to make a lot, because the cement manufacture plant you'll need to buy won't be cheap, I'm guessing. But it doesn't take up much space.
Sounds great for community-based building projects.