WordPress package repository and deployment

I am looking for any documentation on how WP deployment (of WP core and plugins) works, especially the package repository. I’ve done quite some searching, and am still unsure where the repository is, what licence the code is under, ect. What I want to do is create a similar system for another big PHP app.

I am NOT looking for
* The SVN/Git/whatev repository
* How to write an extension
* Where to download extensions