I like developing my own CLIs and installing them using the dotnet tool command. I can then use them to make some manual tasks easier for myself. Recently I started playing with SendGrid Dynamic Email Templates. They have a great user interface but I wanted to do things programmatically.
If you're interested in expanding on it, you can find the source code here. It's open-source so feel free to clone and play around.
I also wrote a step-by-step article (quite long though) to explain how all the tools work together here