Tecadmin published a guide about installing Mono on Ubuntu 18.04 and 16.04.
How to Install Mono on Ubuntu 18.04 & 16.04
The Mono project is sponsored by the Microsoft. It is an open source, cross platform implementation of Microsoft .NET Framework. Mono supports most the modern operating systems with 32-bit and 64-bit architecture. This tutorial will help you to install Mono on Ubuntu 18.04 & 16.04 systems.
How to Install Mono on Ubuntu 18.04 & 16.04