How do I install pgadmin3 using brew cask?
It's necessary to turn on cask-versions, a project mentioned at https://github.com/Homebrew/homebrew-cask-versions

$ brew tap homebrew/cask-versions
Updating Homebrew...
==&gt; Auto-updated Homebrew!
Updated 1 tap (homebrew/cask).

==&gt; Tapping homebrew/cask-versions
Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask-versions'...
remote: Enumerating objects: 228, done.
remote: Counting objects: 100% (228/228), done.
remote: Compressing objects: 100% (217/217), done.
remote: Total 228 (delta 16), reused 51 (delta 10), pack-reused 0
Receiving objects: 100% (228/228), 92.05 KiB | 4.84 MiB/s, done.
Resolving deltas: 100% (16/16), done.
Tapped 208 casks (248 files, 350.3KB).


$ brew cask install pgadmin3
==&gt; Satisfying dependencies
==&gt; Downloading https://ftp.postgresql.org/pub/pgadmin/pgadmin3/v1.22.2/osx/pgadmin3-1.22.2.dmg
######################################################################## 100.0%
==&gt; Verifying SHA-256 checksum for Cask 'pgadmin3'.
==&gt; Installing Cask pgadmin3
==&gt; Moving App 'pgAdmin3.app' to '/Applications/pgAdmin3.app'.
  pgadmin3 was successfully installed!


Also, when the application is first opened, a '“pgAdmin3” can’t be opened because it is from an unidentified developer.' message will be encountered, which can be fixed by opening the application from the application folder, as documented at The app can’t be opened because it is from an unidentified developer