Unity Networking Servers
This is where you can download the latest source code for the Unity builtin networking servers. The current version is 2.0.1f1 (Unity 3.x compatible):
Master Server
For use with the MasterServer.* API.
Facilitator
Required for doing NAT punchthrough, both parties must be connected to the same Facilitator.
Connection Tester
Required for performing connection tests, it needs to be hosted on a server with 4 unique IP addresses.
Proxy Server
Used for proxing traffic from clients to servers they otherwise could not connect to, be aware that this adds a lot of latency to the traffic.
For more information see the Master Server Build manual page.