Downloading Posterous 1.0 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The application lies within Internet & Network Tools, more precisely Download Managers. This software for Mac OS X was originally produced by Petr Fischer. We recommend checking the downloaded files with any free antivirus.
From the developer:
Posterous Backup Tool will download all the posts including photos, videos and audio files from Posterous stream to your local computer. It also creates a HTML overview index pages inside backup folders. Never lose your articles (blog posts) or family photos.
You may want to check out more software for Mac, such as Posterator, Desktop Posters or Poster Maker - Create & print a poster or flyer, which might be related to Posterous.