If you feel like running arbitrary code downloaded over the internet (pypi doesn't support gpg signatures anymore), mat2 is available on pypi, and can be installed like this:
pip3 install mat2
Thanks to kpcyrd, there is an package available on Arch linux's AUR.
There is a package available in Debian and you can install mat2 with:
apt install mat2
Thanks to atenart, there is a package available on Fedora's copr.
First you need to enable mat2's copr:
dnf -y copr enable atenart/mat2
Then you can install mat2:
dnf -y install mat2
mat2 is available in the torbrowser overlay.
mat2 is available on homebrew:
brew install mat2
mat2 is available on MacPorts:
port install mat2