This paper describes the features of the HARTIK system, a hard real-time kernel designed to help the development of real-time applications, ranging from classical hard control systems to soft multimedia, distributed systems. The portability, the predictability and the flexibility in expressing timing constraints allow the application designer to explore a broad set of solutions both from a hardware and software perspective. A toolkit has also been developed to support the design phase. The kernel supports 16-bit and 32-bit Intel 80/spl times/86 processors, DEC Alpha AXP-PCI-33, and can be easily ported to other different hardware architectures, such as microcontrollers and embedded systems. The relevant features offered by the kernel include direct specification of timing constraints, such us period and deadlines, coexistence of tasks with different criticalness, dynamic scheduling of periodic and aperiodic tasks, bounded blocking time on shared resources, prevention of deadlock and chained blocking; asynchronous, time bounded communication paradigm for exchanging data among tasks having different execution rates.