To install HORNET, add the HORNET repository to /etc/apt/sources.list:

deb http://ppa.hornet.zone stable main

And import the key that is used to sign the release:

$ wget -qO - https://ppa.hornet.zone/pubkey.txt | sudo apt-key add -

After that you can install and update HORNET as any other software package:

$ apt-get update
$ apt-get install hornet

Testing builds are available from repo:

deb http://ppa.hornet.zone testing main