Here are some of the most important open source solutions for high-speed file transfer: UDT (UDP-based Data Transfer Protocol): UDT is an open source file transfer protocol that is designed to optimize data transfer speeds over wide-area networks. UDT uses UDP (User Datagram Protocol) to provide a reliable, high-speed data transfer mechanism, and includes features such as congestion control, flow control, and error correction. FileCatalyst: FileCatalyst is an open source file transfer solution that uses a proprietary UDP-based protocol that is optimized for high-speed file transfers. FileCatalyst includes features such as compression, encryption, and file synchronization, and is used by many media and entertainment companies for transferring large files. Aspera on Cloud: While Aspera itself is not open source, Aspera on Cloud is a cloud-based file transfer solution that offers a variety of features for high-speed file transfer, including support for large files, high-speed transfer rates, and enterprise-grade security. Aspera on Cloud also includes an API for integrating with other applications and systems. Tsunami UDP: Tsunami UDP is an open source file transfer tool that uses UDP to provide fast, reliable file transfer over the internet. Tsunami UDP includes features such as encryption, compression, and checksum verification, and can be used for transferring large files or large numbers of files. FileZilla: FileZilla is an open source FTP client that includes features such as drag-and-drop file transfer, support for secure file transfer protocols, and a customizable interface. While not specifically designed for high-speed file transfer, FileZilla can be used to transfer files quickly and efficiently. These are just a few examples of open source solutions for high-speed file transfer. Each solution has its own unique features and benefits, so it's important to research and compare them to find the best solution for your needs.