From https://signup.netflix.com/openconnect/software:

Operating System

For the operating system, we use FreeBSD version 9.0. This was selected for its balance of stability and features, a strong development community and staff expertise. We will contribute changes we make as part of our project to the community through the FreeBSD committers on our team.

Web server

We use the nginx web server for its proven scalability and performance. Netflix audio and video is served via HTTP.

Routing intelligence proxy

We use the BIRD Internet routing daemon to enable the transfer of network topology from ISP networks to the Netflix control system that directs clients to sources of content.