These have been out a while, but they just recently showed up at my local craft store.
http://www.shopatron.com/products/category/228.5.1.1.96753.0.0.0.0
It kinda looks like a lip balm tube, but I would advise against using it that way. I got the black and white set.  Putting it down on paper it initially reminded me of oil pastels. Using water it’s great for doing gray scale work, it’s got a broad range.  The only drawback I found is it diluted a bit too much with water. It also dries very quickly so I no wet in wet techniques. Once this is dry it’s permanent, so it would be good for under paintings.  It’s transparent (which I like) so I definitely would like to try out the color versions and gel mediums.  The price is reasonable (especially if your craft store does coupons) and it’s portable.  So I really like it 🙂