I made this tool in 2002 to extract the Grf resource files of the game Ragnarok Online (alpha version). I reverse engineered the file format by analyzing the files with a hex-editor and guessing the compression used. The files turned out to be compressed with a variant of the LZ-compression algorithm. The program reads a header and extracts all files contained in the source file to the destination directory.
You can download the executable of Grf extractor 1.2. It only works for alpha versions of Ragnarok.