its called aluminum extrusion. available from many places and sizes.
when cutting its important that your cuts actually be 90degrees. I.e. flat and parallel/perpendicular faces. So get the necessary equipment to setup your saws correctly. Its still sorta early days with this stuff, and aquariums(we need a rocket engineers stand thread, someone lays down the law (follow manufacturer spec atm.)) I don't think we have a good consensus on which type of joints or construction (blind, corner cubes, joining plates, various types of brackets, roll vs hammer nuts.) That said make two flat rectangles for top and bottom and connect them. If its a long tank add extra supports both vertical and horizontal. I think 3030(metric) or 1515(imperial) is likely good enough for everything except maybe a MONSTER 300g. There are a ton of cool attachments for these. ultimately its just a modular design so the sky is the limit. Ive been decking mine out with all sorts of 3d attachments. I wanted a floating light so I ran a long extrusion from my stand to a right angle over the aquarium. With how expensive wood has gotten extrusion feels pretty afforable imo, and the extra stand space is great! that said its pretty easy to just trim the whole thing with wood. a couple holes, nuts, and you can easily make it look like a conventional stand. I think this will eventually take over the whole scene.
