Real-time scheduling of semiconductor manufacturing operations, semiconductor test operations in particular, is complicated due to the following factors; multi-head resources, multi-level hardware dependency, temperature and hardware criteria, dynamic determination of processing time and indexing time, batch processing and re-entrant flow. A first-of-its-kind, object oriented (OO), discrete event simulation (DES) toolkit, RTMSim++ for real-time simulation-based scheduling applications has been conceptualized, designed, developed to resolve real-time scheduling problems in manufacturing. This paper reviews the work done in the development of RTMSim++ toolkit, and a case study in a real-time scheduling application. The salient features of the toolkit includes flexibility to customize and extend its functionality, real time shop floor status data initialization, and capability for modeling complex resource and process relationships. In the case study, RTMSim++ has been customized to incorporate very company specific heuristic rules, with the objectives of improving delivery performance, equipment utilization and cycle time.