Catnip is an all-female improv group, which, based on what I've seen so far, is not all that common.*** They are phenomenal. Around here they can often be seen in performance at IO West and Second City LA; they also perform elsewhere. If you have a chance to see them anywhere, you should go!
*** Also not common? Predominately pigmented improv groups. What's cool is at least two of the prime training outlets on this coast will talk about this fact without fear.