Sites and entities, APS planning, and a Mongoose metadata layer with no D365 runtime equivalent.
SyteLine models the business through sites and entities whose statutory meaning has to be settled before anything else, because a site can legitimately become a D365 legal entity, an operational site, or both. Standard, average and FIFO costing may coexist by item and site, which forces disciplined item model group design, while APS global planning and remote-site behaviour do not land one-for-one in D365 master planning. The extension estate — IDOs, Mongoose metadata, extension class assemblies, and application and form event handlers — has no direct target equivalent and must be redesigned into X++ and Power Platform patterns.
Site / entity topology + IDO extensions → Legal entities + sites + X++ extensions