YUI!

Dojo Toolkit is an open source modular JavaScript library (or more specifically JavaScript toolkit) designed to ease the rapid development of cross-platform, JavaScript/Ajax-based applications and web sites.

Intuitive and DocumentedIt is strongly influenced by jquery with many similar methods so you'll feel at ease developing with Umbrella.However there are also some improvements such as with .ajax(), .append(), etc.

MooTools (My Object-Oriented Tools) is a lightweight, object-oriented, web-application framework for JavaScript.

No lock-in, no wrapper objectsDesigned to work with Vanilla JS, not replace it. Light as a featherOnly 3KB minified & gzipped!Chaining without prototype pollutionOnly adds one _ property (optional, customizable) ExtensibleAdding new blissful methods is easy as pie!(Mostly) readable sourceKnow what you’re running. Excellent for learning! Built with modern standardsUse polyfills to extend browser support.

PKIjs is a pure JavaScript library implementing the formats that are used in PKI applications (signing, encryption, certificate requests, OCSP and TSP requests/responses). It is built on WebCrypto (Web Cryptography API) and requires no plug-ins.