MsQuic

MsQuic is a free and open source implementation of the IETF QUIC protocol written in C that is available on both Windows and Linux platforms. The library is designed to be a cross-platform general purpose QUIC library and optimized for client and server applications, for maximal throughput and minimal latency. It supports asynchronous IO.
The HTTP/3 stack of Microsoft Windows is being built on top of MsQuic.
The source code is licensed under MIT License and available on GitHub.