Krypton

Krypton is a free Fabric mod for Minecraft that optimizes networking and entity tracking, with its main performance focus on servers. It can run on both client and server, including dedicated servers. The mod includes optimized Netty handlers derived from the Velocity proxy, with native code where appropriate. Flush consolidation is intended to reduce server CPU use and tick times, and to lessen the impact of speculative-execution hardware vulnerabilities. Smaller optimizations target memory use and packet serialization speed. Krypton is tuned for Linux, although the project says it should work wherever Minecraft can run. CurseForge lists Fabric and Quilt as supported loaders. The maker aims for compatibility with Fabric API, Lithium and Sodium; support for other mods is best effort. The project is licensed under LGPL-3.0-only, and support is best effort without guarantees of stability or compatibility for every setup. The maker describes it as effectively feature-stable, with updates for new Minecraft versions dependent on personal availability and need. GitHub, CurseForge and Modrinth are listed for reasonably stable release downloads.