Signal messenger is an end to end encrypted applications that can be installed on KDE neon and is also available on Andriod, iPhone, Windows and Mac. It's basic functions are encrypted text and video messaging which it does very well and very easily compared to many other applications. Signal is primarily tied to a cell phone number so it will need to be installed on a phone before it can be used on KDE neon.
To install Signal open up Konsole and type,
curl -s https://updates.signal.org/desktop/apt/keys.asc | sudo apt-key add -echo "deb [arch=amd64] https://updates.signal.org/desktop/apt xenial main" | sudo tee -a /etc/apt/sources.list.d/signal-xenial.listsudo apt update && sudo apt install signal-desktop
This will install the key for Signal, add the application repository and finally update and install the program.
After installation you can find in the Applications menu under Applications/Internet or by selecting the menu and typing its name.
Tips and tricks
The major thing to remember with Signal is that it is primarily tied to a phone number. If you wish to keep your old messages, etc.. when swapping phone numbers it is best to create a backup.
This can be done by going into Setting in the menu on the phone application and then selecting Chats and Media. At the bottom of the options there is a backup option you can switch in. It will give you a number that you can use to decrypt the backup if you ever need it. If you lose this number then the backup is useless.
I found this out when swapping phones a while back. Luckily my old phone and sim card were still operational so I was able to go and create a new backup, get a new decryption number and then use that.