In this repo there are a few libraries that you can just copy and paste into TIC-80 and use.
libMenu is a customizable library for creating interactive menu screens.
libGui is a customizable (but small) library for creating labels and buttons (with callbacks) declaratively.
libTimer is a library that allows setting timers with callbacks, similarly to setInterval in JavaScript.
libBindKey is a small framework that allows binding callbacks to specific keys or buttons.
libNameEntry is a library that allows you to read a (short) name from the user, and is compatible with all platforms that run TIC-80 and support the btnp() function