In MsssaRTE OssdfS the FSF services were implemented using the application-defined scheduling API proposed for the POSIX standard. The underlying operating system is based on the traditional real-time POSIX fixed priority scheduling, and we install a secondary application defined scheduler that contains the FSF servers and manages the negotiated contracts. The modules that are currently implemented in MasssRTE OsfsS are the core (using fixed priorities and sporadic servers), shared objects (with the SRP), spare capacity sharing, and the distributed module.