If you're a fan of drinking from the firehose and want a project that includes everything under the sun 🌄, check out the Trello Power-Up Project. It includes an example of almost everything you can do with a Power-Up and the code is highly documented.
Want the absolute bare minimum to get started? We've got you covered! The Power-Up Skeleton project has the absolute minimum required to register a custom Power-Up for a Workspace. Each project's README contains information on getting started with the project. After remixing any of the projects, you should be able to register them as new custom Power-Ups.
Want a written step-by-step guide on building a Power-Up? We've put together a series of tutorials on our blog to help you get started. First post is here.
What about React and TypeScript? Check out App Fox's Trello Power-Up sample here.
Prefer a video tutorial? Follow along as we develop a simple Power-Up to show weather data on cards: