Various systems of extruded aluminum. Mostly t-slot. * [80/20](http://www.8020.net/t-slot-2.asp) * [makerbeam](http://www.makerbeam.eu/) * [openbeam](http://www.openbeamusa.com/) * [makerslide](http://makerslide.com/), 20x40mm extruded aluminum with rails built in (for linear bearing systems) * [gridbeam](http://gridbeam.biz/)