PEP
PEP is an acronym for PDF Editing Program (for Mac). It's a free and open source PDF editor for Mac.
For now, PEP is work-in-progress.
Currently working on the core, a PDF engine called Gene. You can build this app with Xcode, and see the simple rendering result, and if you are interested in the tests, just click Test in your Xcode, if should be all pass.