QGIS install on OSX with homebrew: "You have other linked versions!"

I had the same problem and figured it out. You did brew tap osgeo/osgeo4mac before and thereby expanded your brew with the osgeo-tap. The repository documentation mentions they are currently 'renaming' formulae. It turns out they're renaming formula postgresql to osgeo-postgresql etc. So my trick was to type on the shell:

for f in libgeotiff libspatialite netcdf postgresql gdal postgis sip qscintilla2 pyqt; do brew uninstall --ignore-dependencies $f; done

This will uninstall the currently installed relevant formulas from osgeo. Next, install the formulae with the new name (prefixed with osgeo-) with:

for f in libgeotiff libspatialite netcdf postgresql gdal postgis sip qscintilla2 pyqt; do brew install osgeo-$f; done

Once finished, you should be able to install osgeo-qgis with:

brew install osgeo-qgis

• if it fails with Error: Too many open files @ rb_sysopen , do a ulimit -n 1024 first
• it will take a while, the amount of direct/indirect dependencies is quite large