I love to experiment with open or altered tunings now and then, especially on acoustic. It takes everything I know about shapes and positions and largely throws it out the window. In addition to open tunings (with and without slide), I like to play with altered tunings like DADGAD and dropped D also. I've been listening to some percussive acoustic guys and one of them frequently uses CGCGCD, which is an interesting tuning. What are some of your favorite altered tunings. Feel free to link videos if you have performances with them.