This is a Carrick Mat that I made with olive drab 550 paracord. Here's a tutorial link (updated since the original disappeared), and it's also known as a thump mat.
The original diagram I linked to, showed it being made using your fingers, but I just laid it out on the table to tie it.
I started with about 15 feet of paracord, and after working the slack out, I ended up trimming a couple feet of excess off.
Made with paracord, it makes a nice coaster, a mat to lay your keys/flashlight/knife/multitool on to keep from scratching up your nightstand or dresser, or attached to the top of a boonie hat with a couple of safety pins as another way to carry some extra cord while adding a little decoration to the hat. *Note, if added to a hat, don't get mad if folks ask you what instrument you play in the marching band, lol...
...and another done in GID(glow-in-the-dark) cord from Cool Glow Stuff!. I'll put this one on my nightstand as a coaster for the glass of water I keep next to the bed. If I wake up thirsty in the middle of the night, I won't have to turn on the lamp to see the glass, it'll be illuminated by the mat.