This repo exists to help you out in case you are trying to use / compile a particular revision of OpenFrameworks Master branch roughly between mid 2016 and early 2018.
When you try to run the \OpenFrameworks\scripts\YOUR_PLATOFRM\download_libs.sh script, you will notice it fails (beacuse the script tries to download some zip files from ci.openframeworks.cc that are no longer there).
To solve for this, replace \OpenFrameworks\scripts\dev\download_libs.sh with the download_libs.sh in this repo.
Then go ahead and run your platfrom's download script (ie OpenFrameworks\scripts\osx\download_libs.sh for osx) and it all should work.
See this issue for more info.