LDM-McIDAS is a set of LDM-compatible decoders for products contained in the Unidata-Wisconsin (LDM feed type UNIWISC aka MCIDAS), NIMAGE, FNEXRAD, FSL2, and NLDN data streams that are available by IDD feed to core Unidata sites.
Imagery decoded with LDM-McIDAS decoders is usable by all applications supported by the UPC (e.g., GEMPAK, McIDAS, IDV). FSL2 and NLDN products are decoded into McIDAS-compatible formats, so they are intended to be used by McIDAS only.
If you want to decode the satellite, radar, and satellite-product imagery in the LDM UNIWISC (Unidata-Wisconsin), NIMAGE, or FNEXRAD datastreams, you need the LDM-McIDAS decoders. Furthermore, if you want to decode the FSL2 Wind Profiler data or NLDN lightning data into McIDAS-compatible files, you need the LDM-McIDAS decoders.