ADeelN

What Is This App?
ADeelN is an open source app to cross post to App.net and Twitter. It comes with a share extension to share links (and soon images) to App.net from iOS apps with share functionality. ADeelN is written by Dominik Hauser @dasdom

Minimum System Requirements
Requires iOS 8.0 or later.

Source
ADeelN is written is Swift and it's open source.