RMS: Microsoft Dynamics Retail Management System -- comprised of 3 modules at each store location (Store Operations Administrator, POS, Manager), plus Headquarters for multi-store environments; new license sales to new customers were discontinued in July 2016; however, additional licenses and extended support remains available to current RMS users through July 2021 (reseller support will continue after that date)
RMH: Retail Management Hero -- the successor to RMS built on modern codebase; comprised of 2 modules (POS and Manager); the multi-store replacement for HQ is called RMH Central
RRE: Retail Realm Essentials -- a mid-market platform built on the MS Dynamics AX core
AX for Retail -- an enterprise level platform for large chain stores
RMS/RMH runs on any Windows 7/8/10 PC on a peer-to-peer local network (up to 20 stations); no IT service is required for setup nor is a server OS required or recommended except for a large multi-store operation running HQ with MS stack requirements.
RRE/AX requires the full MS stack (server OS, SQL Server standard or enterprise edition with CAL licenses, etc.). An IT service is required to setup and maintain the in-store and connected infrastructure at all locations and corporate office.