I am running QGIS 2.18.7 on Mac OS (10.11.6). The application crashes frequently. I usually only manage a few minutes work (while saving all the time) before it crashes. I recently upgraded to this version as the last version was crashing too often... glad that helped! There doesn't seem to be any common thing that causes this. Sometimes it crashes when I try to edit a shapefile, sometimes when I open a raster layer, sometimes when I zoom.... endless number of things. I have tried setting up a new workspace, and keeping it trim and none of my open files are exceptionally large. I have tried uninstalling all the plugins.
I have also checked other threads and noticed a few people having these issues, and the only thing that helped anybody was to follow the advice on the install page to rename or move the location of 'Qt4 developer components'. However I have no idea what these are.. or where to find them!! I search in finder and look in the usual places but no sign of these items.