You don't need to use Garmin Express. Most new Garmins work as USB mass storage devices, so you can just copy files on or off.
Garmin Express may be a bit quicker/easier if you want to upload to Garmin Connect, but you can still do a manual upload if you want.
Some of the new Garmins can upload via wifi or Bluetooth, so you would need Garmin Express for that. Yes, there is a Mac OS X version, plus similar things for Android / iOS.