Synergy software, which shares your keyboard and mouse to multiple computers through the network, is no longer available in the Ubuntu 19.04 repos, so the only remaining option is to build it from source:

sudo apt install qtcreator qtbase5-dev cmake make g++ xorg-dev libssl-dev libx11-dev libsodium-dev libgl1-mesa-glx libegl1-mesa libcurl4-openssl-dev libavahi-compat-libdnssd-dev qtdeclarative5-dev libqt5svg5-dev libsystemd-dev git build-essential
git clone https://github.com/symless/synergy-core.git
cd synergy
mkdir build
cd build
cmake ..
make
sudo make install

That’s it, Enjoy!

Note: After starting Synergy, you don’t have to enter the serial to get basic functionality, just cancel and you are good to go.

Source: https://github.com/symless/synergy-core/wiki/Compiling