Homebrew
Fink
Homepage: http://www.finkproject.org
Fink is akin to (and iirc based on) the Debian/Ubunutu apt system: it delivers pre-compiled binaries.
MacPorts
Homepage: https://www.macports.org
MacPorts is related to the older BSD Ports collections: rather than pre-built binaries, it containers pointers to the original source + patches required to make that source work on your platform (and with the other apps that you’ve installed via ports).