Let me start by saying that I did not receive any compensation for writing this post. This is a product that I use regularly and love and have decided to share of my own free will.
It's like Gatorade (or Powerade, or whatever other neon colored "ades" are out there) ...only much much better. It's a little fizzy and has no sugar and is quite tasty (Lemon Lime is my favorite flavor so far). There's Nuun Active Hydration and Nuun All Day. The active hydration variety has tons of electrolytes and is made for drinking during or after activities where you sweat a lot. Nuun All Day has vitamins and minerals and is made for making the water you drink all day taste better.
Although I don't drink it while I'm running, but I sure do think about how good it's going to taste when I have some at home! The only time I have ever craved Gatorade in the same fashion I crave Nuun is when I was running Lost Lake last year and I kept thinking how good a cup of Gatorade was going to taste when I got to the water station at the top...too bad they didn't have any...just water. Bummer!
The ingredient list is pretty short and unoffensive...and there's only 7 calories in each serving. I highly recommend trying this stuff out if you are looking for a tasty post-exercise drink that won't blow your entire calorie allotment for the day. I've also read that it's great for camping and hiking if you are treating your water, it's a subtle way to cover up the taste of chemically treated water.