What hidden gem GitHub (or other OSS) projects do you rely on?

Question

I spend a good amount of time looking through GitHub repos for useful libraries / tools for projects I am working on, usually searching for keywords and sorting by stars.Does anyone have go to projects (libraries, tools or otherwise) that are under-rated from a stars / forks perspective such that they are not as visible as they should otherwise be?

themodelplumber · Accepted Answer

abs-lang.org is a personal favorite alternative for writing shell scripts. Clean & simple & probably not ready for the enterprise, just how I like 'em.