Apple - How to find all macOS applications which are not from the App Store?

The screenshot below shows how to use a Finder search query to find all applications that are not from the App Store. The “Raw Query” condition is kMDItemAppStoreHasReceipt != 1. This is the same, I think, as testing for a directory named “_MASReceipt” as in the answer by patrix. But using a Finder search query should be easier for people not comfortable with using Terminal.

• Applications from the store are installed in /Applications (at least by default), so any applications outside of that folder are not from the store.

• Applications from the store have a NAME.app/Contents/_MASReceipt folder, so you could use (in Terminal)

  cd /Applications
  for i in *.app; do
      [[ -d "$i/Contents/_MASReceipt" ]] || echo $i
  done
  

  to find all non-store applications

The simplest way is to go to the Apple Menu -> "About this Mac...", then click "System Report". In the window that shows up, you can scroll to the Software section, and click "Applications". Apps from the Mac App Store are listed as such.

In the screen shot, Skitch was downloaded from the Mac App Store.