macports-ports

MacPorts is one of the original package managers for that. It compiles software from source (or uses prebuilt binaries when available) and installs it in /opt/local, keeping it separate from Apple's system files, on the ports tree repo (the actual packages), but MacPorts as a project has been running since 2002. Over 30,000 ports available. Tcl-based port definitions. BSD-style.

Fully free. Community-maintained, no paid tier, no commercial entity behind it.

The honest take: most Mac developers use Homebrew instead, and for good reason. Homebrew is easier to use, installs faster (prebuilt bottles for almost everything), and has a much larger community. MacPorts compiles from source more often, which means slower installs but more control over build options and variants. MacPorts still makes sense if you need precise control over compile-time options, if you work in scientific computing where specific library versions matter, or if you've been using it for 20 years and your workflow depends on it.

The catch: the community is smaller, packages update slower than Homebrew, and most online tutorials assume Homebrew. If you're starting fresh on macOS, Homebrew is the pragmatic choice unless you have a specific reason for MacPorts.