What are some Open Source Video Conference software?

I am developing a software for an NGO where they need a Video Conference (like GoToMeeting or WebEx) tool.

What are some Open Source Angular Blog Templates?

I am developing a Hashnode like blog/community portal for my employer. Can you share some Open Source Angular templates?

We have a WPF application (uses MVVM). Now we would like to develop Web version of the application using minimal code changes. What would be the possible options to look for?

What are main differences between NativeScript and React Native?

As a Web Developer, which one is good for developing Native Mobile Apps?

I am familiar with HTML5, JavaScript and CSS3. If I have to develop a mobile app what would be the best approach?

I would like to have same source set for both the mobile and web. I am hearing many options like Angular2, React Native, NativeScript and many more but unable to decide on the technology.