I just contributed to the Tachyons project as I find it to be the most exciting and beneficial design tools I've ever used. If you haven't read Adam's thoughtful and insightful articles on design and CSS, you should right now!
I recently just launched my personal site where I design and re-construct things using nothing but Tachyons. I like to keep myself constrained to just the Tachyons colors and classes for all my work. It has made working on the W3 fun again!