Selectize.js
Selectize is the hybrid of a textbox and <select> box. It's jQuery based and it has autocomplete and native-feeling keyboard navigation; useful for tagging, contact lists, etc.
Sc Editor
A lightweight HTML and BBCode WYSIWYG editor
Filepond
🌊 A flexible and fun JavaScript file upload library
Hide Show Password
Because life's too short to waste time re-typing passwords.
Colorpicker
jQuery UI widget for color picking (similar to the one in Microsoft Office 2010).
Starability
Accessible rating forms with cute animations on top.
Forms Angular
Probably the most opinionated framework in the world
Jasny Bootstrap
The missing components for your favorite front-end framework.
Idealforms
The ultimate framework for building and validating responsive HTML5 forms.
Zxcvbn
zxcvbn, named after a crappy password, is a JavaScript password strength estimation library. Use it to implement a custom strength bar on a signup form near you!
Garlic.js
Garlic.js allows you to automatically persist your forms' text and select field values locally, until the form is submitted. This way, your users don't lose any precious data if they accidentally close their tab or browser.
jQuery Super Labels
Give your forms a helping of awesome!
Color Picker
React ColorPicker
Form
jQuery Form Plugin
Completely
A fresh take on autocompletion for a wonderful user experience
Angular Validation
Customizing Form Valid Message in AngularJS