Haiku

Haiku is a fast, open-source operating system, a community-driven continuation of the BeOS platform, specifically targeting efficient personal computing.

Haiku, originally OpenBeOS, is a free, open-source operating system that directly succeeds the BeOS architecture; development began in 2001. The system is built for responsiveness, featuring a fully threaded design for maximum efficiency on multi-core CPUs and a custom hybrid kernel derived from NewOS. It utilizes the Be File System (BFS), which supports indexed metadata, treating the file system like a database. The entire project (kernel, drivers, toolkit, and desktop applications) is written by a single team, ensuring a unique level of consistency and a cohesive object-oriented API for accelerated C++ development.

https://www.haiku-os.org/