These formulae are only available in head-only versions, and have no stable tarballs.

Just brew tap homebrew/headonly and then brew install <formula>.

If the formula conflicts with one from Homebrew/homebrew or another tap, you can brew install homebrew/headonly/<formula>.

You can also install via URL:

brew install https://raw.githubusercontent.com/Homebrew/homebrew-headonly/master/<formula>.rb

There are a few problems with head-only software:

• Since there's no stable release, the software is liable to change at any moment. We can't guarantee that head-only software will build reliably or be compatible with other software which builds against it, and that increases our support burden.
• Homebrew's version management and upgrade mechanisms don't work with head-only software.

Contact the software's developer and ask them to tag a stable release. If the software has a stable release and works reliably, feel free to submit a pull request at the main Homebrew repository.

brew help, man brew, or the Homebrew wiki.