Etcher is available to download for Windows, macOS and Linux from the Etcher.io website as well as from the GitHub release here.
Etcher’s Linux builds are provided in the AppImage package format for both 32-bit and 64-bit systems.
What are app images? AppImages are self-contained runtimes that do not require manual installation or root access, but do require you give them the necessary permissions to run like so:
Because an AppImage will run on pretty much any Linux distro out there you only need to download it, give it permissions (see here) then double-click on it to run:
If you prefer to install your apps in a more traditional way, i.e. using apt, you can install Etcher on Ubuntu from a repository.
Getting the repo set up is a bit more involved than using the AppImage linked to above but it does ensure you get future Etcher updates automatically through the Software Updater tool.
To add the Etcher repo first open the Software & Updates app:
Select the ‘Other Software’ tab in Software & Updates 
Click ‘Add’  and paste the following the entry field of the box that appears:
deb https://deb.etcher.io stable etcher
Click ‘Add Source’  to confirm the change, then close Software & Updates. You’ll likely be prompted to update your software sources.
You can also add the repo via a terminal with the command:
echo "deb https://deb.etcher.io stable etcher" | sudo tee /etc/apt/sources.list.d/balena-etcher.list
However you add the repo the next step is to add the repository key. This allows Ubuntu to verify that packages installed from the repository are made by who they say they are. You have to add this key to be able to install Etcher as Ubuntu disables unsigned repos by default.
To add the repository key open a new Terminal window, paste the following command, and then hit return/enter:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 379CE192D401AB61
Finally, update your packages list and install the app:
sudo apt update && sudo apt install balena-etcher-electron
That’s it; launch Etcher from the Applications grid