!Rant

For a school project i had to develop a copy of Skype, This had to be able to run in Linux OSx and Windows, Any suggestions about what to use ?
I thought to node js electron for the app and node + mongodb or rethinkdb as a back end

Do you need voice and video? Should it be a stand Alone? If so, i would say something like Java or Python. Else, anything goes

fyi skype-electron in AUR

Electron would be the easiest except if you're already experienced in the other platforms.

Use Python. It's really easy to use. And it has a lot of great libraries that make interacting with stuff like the camera and the mic easy. Also it's socket library is easy to use.

Why don't you just create a webapp like discord has. That will work on any OS just probably not with ie

Yep pretty easy:
1. node
2. electron
3. postgres/mongo
4. webrtc: use SimpleWebRTC lib (take my word)
5. For webrtc use Google's STUN server. Use coturn for TURN server (or you could use a free numb TURN server). Use &yet's Signal Master for signalling server to combine them.

Use webRTC it's simple and elegant. u can find many frameworks which makes prototyping quick..