https://github.com/rigtorp/awesome-modern-cpp
The list includes some powerful yet not excessively large libraries from which one can learn including:
https://github.com/skypjack/entt
https://github.com/taocpp/PEGTL
https://github.com/fmtlib/fmt
I do notice that libraries are constructed a bit differently compared to applications (header only vs header/impl).
I do notice that libraries are constructed a bit differently compared to applications (header only vs header/impl).