Some of my favorite UI libraries:
NumberFlow for animating numbers.
input-otp for one-time passwords.
Liveline for real-time charts.
Leva for customizable GUIs.
cmdk for command menus.
Virtuoso for virtualization.
dnd kit for drag and drop.
Sonner for notifications.
This might sound weird but hear me out:
The essence of what I think a lot of people mean when they talk about "functional programming" is actually simpler than you think:
It's immutability & everything-is-an-expression, and nothing with regards to the type system, per se.