I started learning C#, before that I wrote in java. What open source projects can you participate in?

Question

open source

Actually the question is in the title. It is difficult to decide in which specific direction C # should develop.

Answer 1

By itself, C# makes little sense without the subject matter. C# programmers "in their purest form" are almost never needed. For example, for the Web, you have to learn ASP.NET (which is more than just C#), and for desktop applications, WPF, and so on. Maybe you decide to write mobile applications at all - then look at Xamarin. And vacancies, respectively, will be called, for example, "ASP.NET developer", which means you need to write the web there.
For open source projects (if you really want to) - choose any Microsoft project from github. It's not clear what you want to achieve though...

Answer 2

Decide first. Leading web and mobile application development industries. It is also worth looking at the universal windows applications.

Answer 3

It is difficult to decide in which specific direction C # should develop.

In vyndauz direction... "to develop" ;-)
About open source - to forget.