I have to say - the girls at my work are SO much fun. They do challenges and all sorts of exchanges. It definitely keeps me wanting to stay crafty!
The ATC definition per Wiki is:
Artist Trading Cards (or ATCs) are miniature works of art about the same size as modern baseball cards, or 2 ½ X 3 ½ inches (63 mm X 89 mm), small enough to fit inside standard card-collector pockets, sleeves or sheets. The ATC movement developed out of the mail art movement and has its origins in Switzerland. Cards are produced in various media, including dry media (pencils, pens, markers, etc.), wet media (watercolor, acrylic paints, etc.), paper media (in the form of collage, papercuts, found objects, etc.) or even metals or cloth. The cards are usually traded or exchanged rather than sold.
This is the second round that I participated in and I really forced myself to go outside of my usual crafty zone. I typically don't use stamps, I'm very symmetrical, and all of my colors ALWAYS match. On this card, I used 2 stamps (embossed 1), non-matching ribbon, and a non-matching ink for the second stamp. (the reds on this card match, but it's the only one out of 7.) I'm very proud of how this turned out!!