Caffeine is a livecoding environment for the web. After adding it to a webpage, you can use it to change that page live, without reloading, and to store your changes. You can interact with Caffeine through a full graphical interface inside your page, and with your favorite text editor.
Caffeine's underlying computation engine is SqueakJS, an open-source Smalltalk. From the canvas below this one, you can interact with Squeak's traditional user interface, Morphic. Squeak runs identically on all its host platforms, including macOS, Linux, Windows, and HTML5. You can snapshot a live session on any host platform, and resume it on any other.
Caffeine is also integrated with WebDAV, and with the Chrome Debugging Protocol (CDP). Eventually, Caffeine will have tools for inspecting, debugging, and profiling all the webpages in your web browser, as a full-GUI alternative to the Chrome DevTools. You'll also be able to interact with Caffeine and CDP from your favorite text editor, through a virtual WebDAV filesystem.