One may find abundant examples of free/open source software, and their associated communities of users and developers, by exploring various collections.
These collections go by various names, and have several different kinds of central organizing purposes and principles.
Tools like pip draw from the Python Package Index,
which, as the name indicates, is centered on providing software written in Python (though individual packages may have non-Python dependencies).
Package archives for Linux distributions include
- https://packages.debian.org
- https://packages.ubuntu.com
- https://www.archlinux.org/packages/
- https://src.fedoraproject.org
Oftentimes, these distributions will have one or a few official repositories, as well as a number of ancillary repositories offering some tradeoffs among stability, quality, accountability, etc.
The Libraries.io collection is a sort of meta-collection, tracking package managers across a wide range of language- or application-specific package archives and their associated package management software.