GitHub, among other Git providers, is full of hidden gems that are very helpful to all developers. Some of them are well known, but a lot of them are considered underrated even though they're valuable?

What's a repository that you think developers should know about? It can be an underrated repository with not many stars, or it can be a popular one that you still think more developers should know about.

P.S: 👀 Make sure to check out Medusa, the open source Shopify alternative!