Open Source BSD KCP Software

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.

KumoKyaku KCP is a C# implementation of the KCP reliable UDP protocol designed for high-performance .NET applications. It provides ready-to-use APIs while also allowing advanced users to customize segment handling and memory behavior. The project uses unsafe code and unmanaged memory internally to reduce garbage collection pressure, which is important for real-time systems. It supports Span<byte>, external buffer rental, and a generic KcpCore<Segment> architecture for performance-focused implementations. The library is partly thread-safe, allowing concurrent Send and Input calls while restricting concurrent Recv and Update calls for correctness. It is useful for game networking, real-time communication, and other latency-sensitive C# applications that need reliable delivery over UDP.

java-Kcp is a Java implementation of the KCP reliable UDP protocol built on top of Netty. It is designed for applications that need fast, reliable communication over UDP, especially games, video systems, and network acceleration services. The project includes forward error correction support and aims to remain compatible with other KCP implementations, including C, Go, and a related C# version. Its documentation provides server and client examples, usage parameters, best practices, troubleshooting notes, and performance testing information. The library is positioned as stable enough for real projects and has been used in online production scenarios. It is useful for Java backend developers who need low-latency network transport without giving up reliability features.

xkcptun is a C-language implementation of kcptun built on KCP and libevent2. It is mainly designed for embedded and router-oriented environments such as LEDE and OpenWrt, where lightweight networking tools are often preferred. The project provides client and server components that use KCP-based tunneling to improve performance over unreliable or high-latency network links. It also includes a spy utility, making the generated build more than a minimal two-binary tunnel setup. xkcptun can be built with CMake and supports static linking for easier deployment on constrained systems. It is most relevant to users who need a compact KCP tunnel implementation for routers, gateways, and custom network appliances.