Hijack's goal is to enable general-purpose Operating Systems with intelligent and application-specific policies for managing resources and temporal constraints at user-level without changing the source code of host OS. If a policy embedded within the monolithic host OS is not suitable for some task (e.g. due to QoS constraints, the need for a specific scheduler or disk caching policy), Hijack provides the ability to override that service and re-implement as an executive at user-level. Where customization of the system services is not required, the extensive infrastructure already provided by the host OS can be used. This includes the use of the familiar library and system call interfaces programmers are accustomed to. Such application-specific executives exist at user-level, thus any faults they may exhibit cannot crash the system, or alter arbitrary process address spaces.

Please also see the Composite Operating System, which takes a clean-slate approach to system design with extensibility, predictability, and dependability.