Mabber is a Jabber protocol base web and mobile instant messaging client. Even though Mabber primarily uses the Jabber protocol, they also support MSN, Yahoo, AIM and ICQ. There is also a java MIDP based client for mobile phones which can be downloaded by entering your mobile phone number on the site after which they’ll send an SMS with the applicaion.
Techcrunch says this is a serious competitor to Meebo which is only web based. And the good thing is this site isn’t blocked by Websense at my office :)