Dalton Caldwell, at the App.net Blog writes:
Although App.net has had only paid account tiers thus far, we initially conceived of App.net as a freemium service. It took some time to get to this point, but we are now ready to make this vision a reality. Sorry folks but I've already sent out my existing invites. You must have an invite to create a free account, or you can just subscribe like the rest of us.