I am curious if there are any code libraries that you really enjoy using that have a great public interface.
Similar to how my appreciation for Haskell makes me sad how we still mostly use languages with terrible type systems (though Rust gives me hope), and how Clash ("Haskell on FPGA") makes me sad how prevalent VHDL/Verilog are, Qt in turn makes me sad how we collectively moved to web development for UI needs even outside the Web.