XDelta is a library interface and application program designed to compute changes between files. These changes (deltas) may be used to store and transmit only the changes between files. XDelta uses a fast, linear algorithm and performs well on both binary and text files. XDelta typically outperforms GNU diff in both time and output size, even for plain text files. XDelta also includes a simple implementation of the Rsync algorithm and several advanced features for implementing RCS-like file-archival. XDelta is on SourceForge at //sourceforge.net/projects/xdelta/, and versions can be downloaded from there.