Under the hood? I believe MariaDB, but thankfully, I never had to write a single SQL query. I used Appwrite SDK to do operations like db.getDocument, db.listDocuments, db.createDocument...
The project uses Appwrite as a backend. Appwrite solved problems like database or real-time. After you have the Appwrite backend ready, you can use CLI commands from README to prepare a project for this specific repo (project).
Regarding the question about components, not sure if I understand. I found out all about Appwrite and its services from documentation on appwrite.io
I cloned the Reddit minigame that was available this year's April Fools' Day on the r/place subreddit. Anyone all around the globe can join the journey of painting a canvas with millions of pixels. The main difference, I made it open sourced! Host your own canvas and share it privately only with your community or just share it with everyone!
I built all of this in around 4 hours and the best part, I spent more time on the front end than on the backend. The biggest challenge I expected was how to synchronize 4 million pixels between hundreds of users. Appwrite Realtime server managed everything for me and results show up to 1 million users could use the app at the same time!