Basecamp recently open source Stimulus, their new JS framework. It aims to make sprinkling some JavaScript on your page here an there very easy.

Stimulus is a JavaScript framework with modest ambitions. It doesn't seek to take over your entire front-end—in fact, it's not concerned with rendering HTML at all. Instead, it's designed to augment your HTML with just enough behavior to make it shine. Stimulus pairs beautifully with Turbolinks to provide a complete solution for fast, compelling applications with a minimal amount of effort.

https://github.com/stimulusjs/stimulus

DHH talks a bit on why and how they created it in this episode of the Ruby Rogues podcast.