Open Source C# Reliable-UDP Libraries

Mirror is a high-level open-source networking library for Unity multiplayer games. It was originally based on UNET and has evolved into a stable, modular framework used by many production Unity projects. The library is designed to make multiplayer development easier by handling common networking patterns such as network identities, synchronization, remote procedure calls, authority, spawning, and transport integration. Mirror supports multiple low-level transports, making it adaptable to different game genres and deployment needs. It is suitable for small multiplayer games, cooperative games, competitive prototypes, and even larger persistent-world or MMORPG-style projects. The project is especially useful for Unity developers who want a mature networking layer without building protocol and synchronization systems from scratch.

Lite reliable UDP library for .NET Framework 3.5, Mono, .NET Core 2.0, .NET Standard 2.0. Small packet size overhead (1 byte for unreliable, 3 bytes for reliable packets). Helper classes for sending and reading messages. Always use library sources instead of precompiled DLL files (because there are platform-specific #ifdefs and workarounds for unity bugs). Fast packet serializer (Usage manual). Automatic small packets merging. Automatic fragmentation of reliable packets. Automatic MTU detection. UDP NAT hole punching. NTP time requests. Packet loss and latency simulation. IPv6 support (dual mode). Connection statisitcs (need DEBUG or STATS_ENABLED flag). Multicasting (for discovering hosts in local network). Unity support.