Breve.js - A McGyver toolbox of small bits to speed up vanilla js development / prototyping, especially for toys.
Libraries are useful, but, let's face it, is there one around that has exactly what you need and not more? Are you really keen on learning new API, usually variations on the same age-old stuff? Breve.js has a learning curve that is almost downhill, and packs only the very basic - you're likely to use every single feature in any but the smallest project.
Inspired by (and with thanks to) http://youmightnotneedjquery.com/
Features: mixin and inheritance, custom events, uuid, debounce and throttle, and, as a pure flight of fancy, a polyfill for requestAnimationFrame. It's intentionally basic and conceived for convenience and speed, not abundance of features. Feel free to fork it and remove what you don't need.