Ask HN: What are the best sample databases for Postgres?

In the SQL Server world, Microsoft has always provided a mid-sized sample database (most recently WideWorldImporters, historically AdventureWorks and Northwind). This is really useful for getting hands-on experience with database administration, query tuning, and the like.

I'm new to Postgres and looking for something similar. Postgres people: what are your favourite sample databases for learning+testing?

I noticed that Microsoft has published a Postgres version of WideWorldImporters (https://github.com/Azure/azure-postgresql/tree/master/samples/databases/wide-world-importers) but it seems like a work in progress (to put it nicely).