Best libraries for language study

I have been using Crystal for several months now, and I would like to improve my knowledge of the language (best practices, idioms).
For this purpose, I plan to study some standard libraries or shards, but I would like to have some advice on the choice of the most suitable for this use.
Thank you for your opinions.

a lot of good shards here: https://github.com/veelenga/awesome-crystal

Very nice shard: