> almost a WebUI alternative to a REPL
That's basically how my team have been increasingly using it. Simply connect Livebook to a locally running Phoenix project and you have a Livebook REPL into your server. When you're dealing with complex data, pulling from different sources and have to build up a bunch of context before you iterate on a function it's super useful to be able to break up that code into chunks, take form inputs[0] along the way and document any quirks. We keep a bunch of livebooks committed in the repo to help debug and iterate on the more complex parts of our codebase.