To an unappreciated degree, research both in operating systems andtheirprogramminglanguageshasbeen severely hampered by the lack of cleanly reusable code providing mundanelow-level OS infrastructuresuch as bootstrapcode and device drivers. The Flux OS Toolkit solves this problem by providing a set of clean, well-documented components. These components can be used as basic buildingblocks both for operating systems and for booting language run-time systems directly on the hardware. The toolkit’s implementation itself embodies reuse techniques by incorporating components such as device drivers, file systems, and networking code, unchanged, from other sources. We believe the kit also makes feasible the production of highly assured embedded and operating systems: by enabling reuse of low-level code, the high cost of detailed verification of that code can be amortized over many systems for critical environments. The OS toolkit is already heavily used in several different OS and programm...