networking – Open source network server/client for turnbased Unity game

The .Net framework has all the pieces you need if you’re implementing something yourself, and they’re cross-compatible in mono (although I haven’t tried them explicitly in Unity).

Check out the System.Net namespace. It has everything from raw sockets to TCP/HTTP clients.

Given the turn-based nature giving relatively low-frequency updates (and high tolerance for latency), I’d consider using an HTTP server of some kind with a technique like long polling.