Even if software that made Skype and Kazaa athors are still BETA version, now it is available to all people.
Joost 1.0 that is Beta version is available to Windows and Mac OS users. I think new versions of Joost will realised very soon, because of big downloads amount and new users count. Joost project was started at the beginning of the year.
Joost software you can download here: http://www.joost.com/download/
