Nez aims to be a lightweight 2D framework that sits on top of MonoGame/FNA. It provides a solid base for you to build a 2D game on.
Ranked in these QuestionsQuestion Ranking
Pro Active community
The community is very active, so if you ask for help you'll get it relatively quickly.
Pro Open source
Completely free, no need to pay for licenses.
Pro Cross-platform development thanks to the use of mono and xamarin
Nez is built on top of monoGame and can be used the make games for many platforms (Windows, Linux, Mac, Android or IOS).
Con Just a framework
Meaning there's no visual scene designer so you'll have to write your own.