This is a simple G-hook modified to have a hole at the bottom for tying a small rope to. Specifically made to hook on the fabric tabs on a tent fly to pull them away from the tent and protect it from rain. 

I suck at knots and tying guy lines is always annoying. So now you just tie it once to the hook, and easily slip it on/off as needed. 

It also functions as a regular G-hook to strap extra things onto your pack.