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At present, the OSs (Operating system) employed for WSN (wireless sensor networks) are either satisfied with only one or two application classes or unsuitable for strict-constrained resources. In view of a variety of WSN applications, there is a need of developing a self-adaptable and self-configurable embedded real-time operating system (RTOS). This paper presents a resource-aware and low-power RTOS termed LIMOS. This kernel adopts a component-based three-level system architecture: action (system operation), thread (component) and event (container). In accordance, a predictable and deterministic two-level scheduling mechanism is proposed: 'non pre-emption priority based' high level scheduling for events and 'preemptive priority-based' low level scheduling for threads. Employing the concepts of LINDA language, LIMOS provides a simplified tuple space and a light IN/OUT system primitive-pair to achieve system communication and synchronization. LIMOS is capable of self-adapting to run on two operation modes: event-driven and multi-threading, with respect to the application diversity. The performance evaluation and comparison shows LIMOS has tiny resource consumption and is fit for the real-time applications. Currently LIMOS has been ported on several hardware platforms for different WSN applications.