Comment by cosmicradiance

Yet the open-source community didn't build anything useful at scale on mono/C#. The C# community has still little to compete with Java when building large scale backend applications. I will love to have alternates to Hadoop, Spark, Kafka and other top Apache projects.

C# could have been much more if Microsoft collaborated with other open-source projects instead of actively fighting and killing them by offering the same functionality natively. All this for having a much tighter control over the ecosystem.