C#

.NET Core and Mono open source frameworks, and available IDEs.

C# IDEs in Fedora

IDE License .NET Core Mono Debugger Packaged in Fedora Alternative download
Eclipse with aCute plugin EPL    
Monodevelop LGPLv2   flatpak1
JetBrains Rider Proprietary, free for Education and OpenSource   tarball
Visual Studio Code with C# plugin Binary is Proprietary Source Code is MIT     flatpak1, copr & rpm

1. Download and install using direct link to Flatpak

Installing Eclipse

First install Eclipse and Eclipse Marketplace

$ sudo dnf install eclipse eclipse-mpc

then install the aCute extension from the Marketplace

Installing MonoDevelop

$ sudo dnf install monodevelop

Installing JetBrains Rider

Installing Visual Studio Code

Download Visual Studio Code and the C# Extension from the Marketplace

Summary

JetBrains Rider is the most complete C# IDE, however it is not open source.

VS Code and MonoDevelop work well for .NET Core and for Mono, respectively.

C# via Eclipse is still young and not very friendly for the former Windows developer, but it can be useful if you’re already an Eclipse IDE user.