Dimdim is very close to releasing Dimdim v4.0 which, among other things, will introduce Mac Desktop Sharing, or "screencasting" as they call it (it's like iChat's Mac Screensharing but totally inside a web browser) And the good folks at Dimdim want this new feature (along with recording, multiple presenters, and other goodies coming soon) to be the best it can be.
If you are interested in helping them test this new Mac feature, please sign up for Dimdim (it's totally free) then send an email with your Dimdim ID and they'll sign you right up. Act fast as they are only letting in a handful of Mac testers right now.
BTW, I'm curious. Has anyone ever beta tested Mac software before? If so, please share what software you tested using the comments feature of this blog.