At first glance, these look like Wedgits, and indeed the original design is a product of the same fertile Swiss toy company, Naef Spiele AG. Wedgits are based on the Diamant design, these are based on Cubicus.
And there you have it, as you can easily decode from the Naef names, this construction set is based on cubical shapes, while Wedgits are based on the rhombus (or diamond) shape. As it turns out, that makes these perhaps a bit easier in some ways, but also probably less versatile.
The bottom line is that both are fun, each in their own way. And their similarities are sufficient that if you like one, you will probably like the other. though Wedgits are much better for an extended enthusiasm, while these are more appropiate for an occasional diversion.
Availability is another matter: Wedgits are available widely, and the only place I am aware of with this set is Seattle's Math'n'Stuff - fortunately for me, they are not far from my home. Fortunately for you, they also sell online (this item isn't listed on their web site, but I have seen it there recently, so inquire).
The set consolidates into a 4" cube which fits snugly into a box that unfolds to show sample designs on the inside and outside. (One panel also shows their "Triangle" product - which is a poorly made version of Wedgits and should be avoided.)
Good Block Play.