Download Master Server Kit FREE Unity. 

Master Server Kit is a complete library that allows you to host your UNET-based multiplayer game on a dedicated server.

Official documentation
Forum thread

Features

– Player registration and authentication (which can be bypassed if desired).

– Guest mode.

– Support for both world-based and room-based games.

– Matchmaking supporting public and private games. Independent game server instances are dynamically spawned and destroyed as needed.

– Zone servers that allow you to distribute the game server load across different machines (useful for load balancing or region-based matchmaking).