Grapple

Grapple is designed to be a simple network layer, allowing the addition of multiplayer features to a game (or other application) for as little as a dozen lines of code. However it is also fully featured, so if you want more from your networking, you can have it.

Basic Features
Simple client-server networking
Keeps all clients aware of all other clients
Passworded servers
Data transfer via TCP, UDP, or reliable UDP
Synchronised variables, allowing use without messages

Advanced Features
Network messenging by either a push or a pull model, or a mixture of both
Multiple methods of querying users
User Groups for client bandwidth saving
Network load reacting data transmission and retransmission
Background pinging to monitor network states
Server failover
A fully functional lobby system
NAT traversal using STUN and TURN