This is a generically useful structural element. It can be used as a container, part of a large structure, electronics enclosures, and various other useful elements. And it can be made *fast* with minimal tools. What you need is:
box cutter, razor blade or scissors
a cardboard box
One cardboard box can make a large number of these, enough to build up a decent structure.
Step 1: Mark and Cut the Corner
The main component of this thing is the corner of a box. We're going to use the fact that boxes have corners that are already bent to our advantage. If you already have made one of these, just trace that out on the corner and cut that out. If you haven't made one and this is your first just slice off the end of a tab on the top of the box and use it as a straight edge to draw lines for equal rectangles on each side of the fold. About 3 inches by about 18 inches, judged by eye should do it. When you finish this step you have two equal rectangles of cardboard linked by a bend joint that we got from the original box shape.
Also, to keep things even, I generally just trace on side, cut it out, then fold it over and run the marker along the folded over edge, and then also use that as a straight edge for the box cutter blade, making for good symmetry.
Step 2: Trace and Cut Out the Third Side
Using the part from the previous step as your template, trace a rectangle identical to one side of the hinge part. Cut that out, compare and fix as needed so you have three identical rectangles, two of which are joined in one hinge.
Step 3: Join and Tape
Form the smaller part as the third side of a triangle with the other part, which should be a roughly equilateral triangle in cross section. Push the sides together tightly with your hands and feet and wrap duct tape around being sure to apply tension on the duct tape enough to really squeeze the joints together. You only need to do it at the ends, but if you want a sealed tube you could wrap the whole thing. Packing tape also works for this job, and you'll want to use that anyway if you're putting art into this.
Step 4: Cut Out Holes for Connector Ties
I make the holes as equilateral triangles about 3/4 of an inch to an inch and a half in size. This can be done very quickly with a box cutter, just making a series of stabbing motions with the correct angles. Exact position and dimension should not matter here, just place as needed for your application.
Step 5: Decorate, Connect to Other Parts, Document and Spread
Since packing tape works just as well as duct tape for this, you can make artistic decorations on paper, paste that to the cardboard, and wrap the whole thing in clear tape. This can be used to give the user an informational link back to instructions on how to make the thing and how to use the thing, thus making it self-replicating. Tracing the end onto another piece of cardboard, cutting that out, and taping it over one end turns the tube into a useful storage and carrying container, which can be dangled from a clothesline and worn on the body, a bicycle or other machine.