Contribute

Needed:

Minetest is in need for a new Mac OS X maintainer. The latest version is in here; it is very outdated: https://github.com/toabi/minetest-mac/, forum topic

Donate:

You can donate money for covering hosting costs and other things.

Users: Modders:

You can create content to the game independently via mods.

Developers (serious stuff):

The core development discussion usually happens on #minetest-dev on Freenode.