Since 0.24.2 has been released, there are nightly builds of Crystal available. Yet, currently, they are not easily accessible without digging through circleci's build output (docker tag nightly
being a notable exception).
If you want to install nightly builds locally, there is a shell script which retrieves the tarball from circleci's API and installs it locally: https://gist.github.com/straight-shoota/a2f4b29203936c04c578d6f6a1ad5f9b