Quicksilver is also a Mixmaster client, used for sending anonymous emails through anonymous remailers.
Other clients include the original Mixmaster command line interface and JBN.
Quicksilver will automatically download capability strings (tell you what a remailer will do), public keys, and statistics. It will also automatically update the client software if you dont have it installed. In fact, you can just download QUicksilver, and it will download Mixmaster for you.