Download of LinkBack 1.0.3 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. The software lies within Developer Tools, more precisely DB Tools. The actual developer of this free software for Mac is LinkBack Project.
From the developer:
LinkBack is an open source framework for Mac OS X that helps developers integrate content from other applications into their own. A user can paste content from any LinkBack-enabled application into another and reopen that content later for editing with just a double-click. Changes will automatically appear in the original document again when you save.
You may want to check out more Mac applications, such as Barcody, LaTeXiT or Nisus Writer Express, which might be related to LinkBack.