What is it? A flat, modular vehicle chassis in which all steering, suspension, motor, gearbox and braking functions are bundled up into removable, replaceable "corner units" in the wheels.
These corner units have built-in electronics so that every single function can be fully electronically controlled. It's not just drive-by-wire, it's steer-by-wire, brake-by-wire, everything-by-wire. So you can put a steering wheel and pedals in if you want, but it's just as happy to take instructions from an autonomous drive system, or heck, even a remote control. There's no difference as far as the chassis is concerned.
What could it be used for? Well, just about any kind of electric 4-wheeler. The big, flat battery pack offers a genuine "skateboard chassis" on top of which your vehicle design options are just about unlimited. There's no other chassis so flat, or that offers so much room for whatever kind of body you want to stick on top, be it a car, van, small truck, big truck, bus, automated delivery vehicle or crazy off-roader.
The corner units can be specified with a ridiculously wide range of options. Active suspension? No worries. 4 wheel steering? Piece of cake. How much ground clearance do you want? How much power? Desired torque? Top speed? Two or four wheel drive? Coming right up. REE can turn these things into just about anything, thanks to a network of relationships with tier-one component suppliers like KYB, Musashi, NSK, American Axle, Mitsubishi and others who are signed up to develop components specifically for these modules.