These formulae are only available as pre-release versions and have no stable tarballs.

There's a few problems with devel-only software:

• Upstream doesn't consider it stable yet so we shouldn't be recommending it to users.
• Things are more likely to dramatically change or break and that adds to our support burden.

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 install --devel homebrew/devel-only/<formula>

Or brew tap homebrew/devel-only and then brew install --devel <formula>

Or install via URL (which will not receive updates):

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

brew help, man brew or check Homebrew's documentation.