The OSE Soft Environment, a tool for simulation and operation of the OSE real-time OS, is claimed as the first simulation environment that can work within a running system. The Soft Environment simulates not only the OSE Kernel's real-time characteristics, but also the tools used with the kernel for product development and maintenance. It operates on a target as well as on the host in a running application.The software is capable of interacting with the whole system while simulating only a part of the system. Its use can also save CPU resources for time-critical parts of an application running on the target system. A GUI provides representations of both host and target.