Cauldron is a cross-platform desktop client for App.net.
If you want to quickly check your messages on App.net while on the go, use one of the awesome mobile clients other people have made, but when you get back home, fire up Cauldron and immerse yourself completely in the App.net experience with an application that's neither light-weight nor mobile, but was instead tailor made for desktop computers and exclusively for App.net.
Posts are shown in columns - open as many as you like, rearrange them by dragging them around.
A little number above every column notifies you of new posts.
Conversations can be viewed in a tree view, making it easy to see who replied to whom.
Add some pictures to your posts, Cauldron fully supports uploading pictures to your App.net storage.
Cauldron is in public beta since April 2013 and will continue to be in beta for a few months after that, but it's stable and has all the important features with more being added every week, so right now is the perfect chance for you to give it a try and use it completely free of charge.