This package contains a PERL script which selects, from an ODF, images taken with the OM grism filters (if present) and processes them using a chained sequence of SAS tasks to produce OM grism spectral products. Omgchain calls a number of SAS packages that prepare the grism images for processing (e.g. insert necessary keywords into the file headers, correct images for distortion, rotate them to optimise spectral extraction, etc.), detect point-like and extended source/spectral features in the OM Science Window (OSW)s, identify and extract spectra within the OSW and then generate corresponding products (FITS-files and plots in PS and PDF formats).