The other answers are right, just explaining in simpler language in case anyone needs it:

Codeberg, like Gitlab and Github, is a site for hosting and managing code repositories. These make it easy for many people to collaborate on a software project, review code, keep track of changes and history, keep track of bugs and feature requests, and more.

Here’s an example of a (very active) code project to explore: https://codeberg.org/tenacityteam/tenacity (An audio editor based on Audacity)

The most famous code repo management tool, GitHub, was bought by Microsoft a few years ago, so reliable community-run alternatives like Codeberg are increasingly important.