We’ve written a blog post summarizing the changes in this release: https://crystal-lang.org/2019/09/23/crystal-0.31.0-released.html
The full changelog is here: https://github.com/crystal-lang/crystal/releases/tag/0.31.0
All the usual installation methods still apply: https://crystal-lang.org/docs/installation/
Docker images and 64 bits Linux packages are available as usual.
The brew formula PR is in https://github.com/Homebrew/homebrew-core/pull/44516