I drew this in an art tool called Hexels Pro that I co-created with my friend Ken Kopecky. Here's a speed-paint video of the piece being painted. (3 hours sped up to 12 minutes): [link]
Hexels is a new kind of art tool that we've been working on together since 2011, and we've finally released it! It's grid-based and it lets you paint with shapes like hexagons (hexels), diamonds, triangles (trixels), etc. You can make your own shapes in the pro version with the custom shape editor. This piece was drawn with the trixels shape mode in Hexels Pro.
UPDATE: Download Hexels (it's freeee!) or buy the pro version here: [link]
And here's a collection of rad stuff that people are making with it [link]