Ask HN: What libraries have you used in more than one project?

I'm putting a list together of toy projects to do.

I like using SDL for toys apps that require graphics, SQLite for database, zlib for compression, etc. Also on my list is

- curl - image libs (png, gif, jpg, webp, svg, tiff, etc) - I would like to try using a audio/video codecs lib with a standard interface for all the videos

QR code I've actually used more than once. What else might I try in a toy project? I prefer it to be standalone with little to no dependencies. I hear I should give zstd and brotli a try. I can't think of anything else so I'm writing this post