Finally! I managed to get invited to Forrst 
I applied a couple of weeks ago, and have been tweeting about it, and was finally accepted yesterday. Here’s the email I recieved:
Hi <my email address>, Your friend Kyle Bragger thinks you should join Forrst. Forrst is part community, part microblog made especially for designers and developers like you. Ask questions, share interesting links, clever code, and inspiring screenshots with your peers. Sign up here: http://forrst.com/signup?i=<random numbers> Love, The Forrst Team This email was intended for <my email address>.
So, at first I wondered who this Kyle Bragger guy was, but after a little looking he is actually the owner of Forrst. So either you get invited by him when your beta application is approved, or he invited me because I tweeted him.
I’m trying Forrst out atm, and I’ll post more here when I get a chance.