It is 80/20 QuickFrame with associated connectors. We have used it extensively since 2006. Just go to the 8020.net website and look at their QuickFrame lineup. The connectors come in all sorts, corners, Tees, etc. and in black or gray. The QuickFrame tubing is fairly light (~.25/ft) and annodized so it looks better than regular extruded box tubing. It has longitudinal ribbing inside that grips the connectors so you just cut it on a miter saw and hammer the plastic connector in with a rubber mallet. Otherwise it is basically pretty similar to thin wall (1/16") aluminum box tubing. The weight of the connectors can add up though. For extra strength we add rivets here and there on the connectors as needed. Works great!
I am surprised the 80/20 QuickFrame isn't more popular in FIRST than it is. It is half the weight of 1010 T-Slot so many teams are so fond of. The QuickFrame also interfaces/connects nicely with the 10 Series if you say wanted to use the 10 Series on your frame/chassis and the lighter box tubing on your upper structure.
80/20 gives all FIRST teams a huge discount on all their stuff so we can actually buy the QuickFrame tubing cheaper than we can buy regular thin walled 1" 6061 AL box tubing. You can always just use the tubing as you would regular box tubing without using the plastic connectors and just weld it up, bolt it, or whatever you want. We've done that too over the years.
We used up over 200 feet of the QuickFrame tubing this year alone between the prototypes, practice bot, and the bot as shipped.