I don't want to ask dumb questions and I also read the content on their site, but I'm still not sure if it's just a twitter alternative or more. And what about identica? Isn't it a similar service like app.net?
>>shell0+(OP)
My understanding is that yes, identica and app.net are similar, except for their business models. Identica didn't have a clear business model (AFAIK), so they would likely resort to advertising. App.net is trying to avoid that by charging users directly.