.NET is a free, cross-platform, open source developer platform for building many different types of applications.
Programmatically drive PS Core with C# (mostly Exchange Online Powershell 3 and later)
GoNorth is a story and content planning tool for RPGs and other open world games
Bot Framework provides the most comprehensive experience for building conversation applications
Workflow Server is a ready-to-use Workflow Engine-based application that you can deploy into your infrastructure