What go-to libraries, frameworks, tools, or otherwise would you say belong in almost every JavaScript developer's toolbox?

There are a ton of JavaScript libraries out there, and while it's always great to have options, sometimes it can be difficult to stay on top everything. To try to bring together a list of tools that match the current landscape, what would you say are your core go-to libraries? Be it new or old, widely used or completely unheard of, what do you feel are the tools almost every modern JavaScript developer should be familiar with?