SEAlink is a file transfer protocol that is backward compatible with XMODEM but features a sliding window system for improved throughput. SEAlink was written in 1986 as a part of the SEAdog FidoNet mailer written by System Enhancement Associates, creators of the famous ARC program. It was licensed with a simple "give credit" requirement, but nevertheless was not very widely used except in FidoNet mailers. SEAlink, and most other XMODEM enhancements, were quickly displaced following the introduction of ZMODEM.