SABnzbd is a free/open-source cross-platform binary newsreader written in Python.

It simplifies the process of downloading from Usenet dramatically, thanks to its friendly web-based user interface and advanced built-in post-processing options that automatically verify, repair, extract and clean up posts downloaded from Usenet. SABnzbd also has a fully customizable user interface, and offers a complete API for third-party applications to hook into.

Read more about it www.sabnzbd.org