These little cubes are easy to make and easy to assemble and as a bonus there are a great many variations you can make and discover. I came to this design myself, however I do feel like I have reinvented the wheel. If your googlefu is stronger than mine please let me know who I should be attributing the basic design to.
This design is based on the diamond window cube by Simon Lewis as per the instructions posted by @ivan-g it only requires 3 units.
Instructions for folding the unit:
Fold two opposing edges into the middle.
Fold the edges back on themselves.
Fold the topmost smallest edge back on itself.
Turn the unit over and fold towards the centre.
Fold the unit in half colour side out.
Fold the ends into the middle.
Make the folds very firm for this last step.
Construction part one:
Lay your three units out and on the 2nd panel on the bottom half draw an A. On the first panel you can draw two little A's as shown or just mark the very end in texter.
Arrange as shown and hide the A's.
Construction part two:
Turn the model over and tuck the purple unit into the 3rd panel of the red unit. Tuck the blue unit into the purple and finish by tucking the red unit into the blue and you are all finished.
Happy folding, Grace.