In this book, I have focused on Microsoft technologies, mainly because I love the Microsoft technology stack. The tooling is great, the languages are evolving beautifully, and in the past few years Microsoft has taken giant steps toward working with the community and putting effort into going open source. Because Microsoft is a big company, it also has a lot of capacity to push out great products at a steady pace. There are a variety of products, and they all work together well, so unless you really want to, you do not have to leave the .NET ecosystem for anything.
However, ...