It’s simply a 3-D design program whose only function is to help you design a chair. That allows for a super-simple UI, which anyone can use–for example, you can add a curving, high back to a chair simply by clicking an dragging. And when you’re almost finished with your design, you can model the chair for how it would respond to a persons weight or see if its proportioned correctly by having the program to place your creation alongside real-world products.
When your design is done, you can then print out templates for cutting out a little paper model–and then send the drawings to a laser cutter, to realize your design in plywood.
Obviously, it’s gonna take a few more interations for programs like these to produce truly beautiful, polished designs, but as a first approximation of a Brave New World of DIY design, it’s pretty impressive.