Stem is somewhere between a framework and a library. It offers a set of classes and functions for all the standard scenarios you can encounter in modern web app development, with design patterns designed to work together.
You can either just download the source from git or from the npm repository as the stem-core npm package:
npm install --save-dev stem-core
If you want to quickly set up a new demo app, you can try to use the create-stem-app npm package:
npm install -g create-stem-app
create-stem-app your_app_name
The Stem code is designed to be used as ES6 modules. The code is meant to be included in the build path for whatever bundling tool you use (webpack, rollup).
The world is full of them. Most of them are mediocre though, and I wanted to show some effort into another direction. The architecture isn't optimized for cool one-liners, but for maintenance and flexibility, that keeps intentionally as much of the functionality in non-core code as possible.
Check out the docs at https://stemjs.org/docs/. This framework is being used for about a year at https://csacademy.com/, and it really works a lot better than any other solution out there.
There's a lot of functionality implemented in Stem. The closer to the core code you go, the better is gets and will probably be clean-up and more commented in the future. You can check out UIBase for the basics of the UI framework. It's an OOP based architecture that piggybacks on the jsx synthax (although you can use it with plain JS). I also included the base state classes that we use to store instances of DB-backed objects in the browser. It's a simple alternative to Redux/Flux if you will.
The Stem code is released explicitly under public domain (AKA The Unlicense, I just like public domain more than the term "Unlicense"). There are no ugly copyright headers you need to keep, and you can copy/paste the code without any attribution. It make it easier to bundle your code, so you know a minimized production js can strip all comments away. In case you need extra assurance, this software is also licensed under Creative Commons 0 (https://creativecommons.org/publicdomain/zero/1.0/), you can pick your preferred license.