As you may know, Franz is an open-source (starting with Franz 5) messaging app available for Linux, Mac OS X and Windows system and it supports a lot of messaging services, including Slack, WhatsApp, Facebook Messenger, Telegram, Skype, Discord and many others.
A full list of supported services can be found here.
The latest version available is Franz 5.0, which is currently a beta release.
I use the application everyday for WhatsApp and it runs quite well.
For Ubuntu 18.10 Cosmic Cuttlefish, Ubuntu 18.04 Bionic Beaver, Linux Mint 19.x, Linux Mint 18.x and other Ubuntu derivative systems, Franz is available as a deb package, so installing it should not cause too many programs. You need to download the deb package and install it via your default package manager. I prefer to use gdebi, as a good habit, because it also handles dependencies.
So this is what you need to do in order to install Franz on your 64 bit Ubuntu or derivative system:
$ sudo install gdebi
$ wget https://github.com/meetfranz/franz/releases/download/v5.0.0-beta.22/franz_5.0.0-beta.22_amd64.deb
$ sudo gdebi franz_5.0.0-beta.22_amd64.deb
Optional, to remove franz, do:
$ sudo apt remove franz