HelenOS is a microkernel-based multiserver operating system designed from scratch. It decomposes key operating system functionality into many isolated, intensively communicating server processes that reside entirely in user space. HelenOS thus provides a computing environment that has several virtues, such as flexibility, increased robustness, well defined explicit interfaces and reduced complexity of individual components as compared to other operating systems. HelenOS runs on seven different processor architectures, ranging from a 32-bit uniprocessor little-endian ARMv4 to a 64-bit multicore big-endian UltraSPARC T1.