Open-source, reusable code, perpetually works in progress to some degree.
This was one of the first front-end features I wrote when I was getting into open source projects, and I've got a soft spot for it. bbuttonbase quite simply standardizes the presentation of interactive elements (including anchors, inputs, and buttons) to appear as simple text hyperlinks by default, but potentially as all kinds of different interactive symbols (buttons, levels, switches, etc.) It does not provide any particular style for this, it simply provides a sensible base to make further customization more convenient.
ViewMan takes a list of elements, and allows you to show one and hide all the others. By preventing the default show/hide behavior of the on-change event, you can more abstractly do *something* to a subset of a group of elements, and *something else* to the other elements in that group.
A very concise little snippet of code that reflects input radio and checkbox's checked or unchecked states in their associated label(s), through adding and removing a class.
Using David Atchley's EventEmitter as a foundation, CustomEventDispatcherJS provides an ES6 class for custom objects to extend, and adds familiar functionality to attach and remove event listeners, as well as dispatching events at will.
Matt Lohkamp's Resume is available as a Google doc.