mmBibTeXExporter is a BibTeX-Exporter-Plugin for Papers.
Papers: http://mekentosj.com/papers/
Papers SDK: http://www.mekentosj.com/papers/plugins/papers_sdk.dmg
This project is based on the SDK's example code, see:
Papers SDK > Sample Exporters > BibTeX Exporter
Installation:
$ git clone git://github.com/muellmat/mmBibTeXExporter.git
$ cd mmBibTeXExporter.git
$ xcodebuild -configuration 'Development + Install'
Now (re)start Papers...