This is a Homebrew tap repository that provides a few formulas (i.e. package definitions).
In other words, it lets you install tools such as elm-new like this:
brew install simonewebdesign/tap/elm-new
Or, to upgrade:
brew upgrade elm-new
This is the generic shell command to run in order to install any formula from this tap:
brew install simonewebdesign/tap/<formula>
Or, alternatively, brew tap simonewebdesign/tap and then brew install <formula>.
You can also install via URL, but you will not receive updates:
brew install https://raw.githubusercontent.com/simonewebdesign/homebrew-tap/master/Formula/<formula>.rb
For more info about Homebrew, run brew help, man brew or check Homebrew's documentation.