C#

.NET

Install .NET Core for Linux.

wget -q https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb
sudo dpkg -i packages-microsoft-prod.deb
sudo add-apt-repository universe
sudo apt-get install apt-transport-https
sudo apt-get update
sudo apt-get install dotnet-sdk-2.2

Check that installation worked:

dotnet --version

Should version should be 2.2.x

Monodevelop

sudo apt install apt-transport-https dirmngr
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb https://download.mono-project.com/repo/ubuntu vs-bionic main" | sudo tee /etc/apt/sources.list.d/mono-official-vs.list
sudo apt update
sudo apt-get install monodevelop

Usage: Navigate to project folder in terminal and run `monodevelop <some_project>.csproj`