If your going to use an open source alternative .NET "framework" I would recommend Nancy
Nancy has a significant amount of community activity and if you look at the commit history you see it's actively being worked on.
It's a significantly more lightweight web framework that's similar to Ruby's sinatra. This means you can use it to handle the basic web things you need
- Interaction with HTTP servers
The goal of the framework is to stay out of the way as much as possible and provide a super-duper-happy-path to all interactions.
It's a lightweight cross platform framework that does the minimal amount you need, doesn't dictate anything about the application architecture you should be using and then just get's out of your way.