Ask HN: What to use for prototyping metal structures?

Is there a product between Erector sets and 80/20 extruded aluminum?

I.e. generic components for building structure that are easy to disassemble and modify during prototyping and sturdy enough to hold against a couple pounds of spring tension or server motors. But targeting a finished product around 1-3 feet on a side on more of a hobbyist budget.