An easy modular by Fumiaki Kawahata.
A very nice modular origami that has the possibility of being expanded.
A very easy modular for once, by Jeff Beynon.
Another modular origami, from David Brill.
A simple modular origami that is very difficult assemble.
A modular box with its lid, by Tomoko Fuse.
Modular origami by Thomas Hull, five tetrahedra inside each other.
A useful and easy origami, make a box out of a single piece paper.
How to make a shuriken/throwing star.