My side project https://totalrealreturns.com/ is now about 5k lines of Crystal. There are some rough edges: in particular I think it could use a better templating solution (a port of HAML would be ideal!), and there are some failure modes with the Redis connection pool that have required workarounds.

This includes unit tests: the built-in spec framework is great and much like rspec. https://crystal-lang.org/reference/1.6/guides/testing.html

I'm now starting to use Crystal for internal backend infrastructure and microservices.

For anyone who wants to kick the tires on Crystal, I built a crystal-docker-quickstart project template: https://github.com/compumike/crystal-docker-quickstart works without having to install anything locally. (Assuming you have docker.) You can have your own, home-built "Hello world" static binary in under a minute:

    git clone https://github.com/compumike/crystal-docker-quickstart.git my_app && cd my_app && ./d_dev
    # in the shell that appears:
    make && out/my_app

Then just edit src/main.cr and you're off and running :)