Name of software:
dotnet
Homepage:
https://dotnet.microsoft.com/download
Why we should include this into the repository:
It is required for cross platform c# development.
Is it open source?
Yes fully, and it's source code is hosted on github.
The main source repository is here but they also provide a source build repository to make it easier to package here
I would be happy to package it myself if this tutorial video is up to date.
Also it is compiled using it's own runtime so it will be necessary to allow a web call to download the dotnet binary to build it.