While you can use nearly any package or library on Replit, we have also built several of our own. You can read more about these here.
Replit web is a Python web framework that is integrated with Replit DB and Replit Auth. It extends Flask, so if you're familiar with that you'll find it very intuitive, and have access to Auth and a DB by default.
Replit Auth lets you easily build a "Sign in with Replit" option to your own applications. If a user has an account with Replit, they can use that to sign into their account on your application too, similar to what you might be used to from "Sign in with Google" or "Sign in with GitHub" options in many third-party services.
Replit audio allows you to interact with audio from your Replit apps, playing sound files, playing and pausing, and navigating tracks.