The Ultimate Free Chat Plugin For BuddyPress

It does exactly what it says and it uses your themes CSS to style it unlike many other free options. Also, it is designed to work ith BuddyPress, unlike others. I am 100% convinced through lots of personal experience (been using this since it came out) that this is the best maintained, most coherent, and most intuitive message plugin out there, even over some $30 dollar ones.