This is the Spider Man 'webslinger' built by Patrick Priebe of Laser Gadgets. Except instead of shooting actual webs it uses a little coilgun to shoots darts. It looks dangerous, and there is no doubt in my mind I'd find a way to shoot myself in the hand and/or face trying to use it. I'm not that coordinated. Did I ever tell you about the time I was in a knife fight? Well I was never actually IN the fight, I slipping in the shower that morning and threw my hip out. I was at the hospital getting a wheelchair when all my buddies came in with stab wounds.
Keep going for a video demo.
Thanks again to Marcus O, who agrees you should probably not try to hang from a building with that. Totally kidding, I say go for it.