Syncthing is one of those programs that really makes open source software stand out. It gives you the ability to synchronise your computer with another computer without having to have a server to negotiate the connection. Eg; You change a file on you computer and the file will update on the other.
To install Syncthing on KDE neon or Kubuntu 18.04 open Konsole and type,
sudo apt install curl apt-transport-https
This will install the curl command and the other package gives apt the ability to download from https secured repositories.
Then add the Syncthing signing key to your computer with,
curl -s https://syncthing.net/release-key.txt | sudo apt-key add -
And add the repository to your sources with,
sudo su -c "echo 'deb https://apt.syncthing.net/ syncthing release' >> /etc/apt/sources.list.d/syncthing.list"
After this you can update and install Syncthing using the command,
sudo apt update && sudo apt install syncthing
So now you Syncthing installed and you can go and start it using the Application menu. There it will be found under Applications/Internet. But really the best way to use it is to start it at boot so you don't have to worry about it. This can be done adding it to the services that start under systemctl.
You can add Syncthing to the list of services to start with,
sudo systemctl enable syncthing@<username>.service
Remembering to replace <username> with your own <username>. Having enabled the service you can then start it with,
sudo systemctl start syncthing@<username>.service
Or check it's status with,
sudo systemctl status syncthing@<username>.service
Generally the program is used in the browser though and as long as it has installed properly you should be able reach it at http://localhost:8384 or by selecting the button below.
Tips and tricks
This is an incredibly handy program. For instance, I have two laptops and using Syncthing I can keep them backed up, without effort, wherever I go to the point they last synchronised.
Having Syncthing on one machine doesn't do anything though. It needs to be on two at least (follow the installation instructions on all the computers) and then you need to join the two installations together. This is relatively easy as it will detect other installations on the same LAN and ask you if you want to try joining. Afterwards, you will join on the other computer as well.
After that it is a matter of choosing which folders you want to synchronise. There is a default Sync folder which will be created but if the folder already exists it will just synchronise the contents across. For instance, after sharing my Desktop folder via Syncthing I then go to the other computer and accept the share and since the folder already exists it doesn't create it, it just updates it.