BeOS is an operating system for personal computers which began development by Be Inc. in 1991. It was first written to run on BeBox hardware. Unlike some other operating systems of the time, BeOS was written to take advantage of modern hardware. Optimized for digital media work, BeOS made full use of multiprocessor systems by utilizing modular I/O bandwidth, pervasive multithreading, preemptive multitasking and a custom 64-bit journaling file system known as BFS. The BeOS GUI was developed on the principles of clarity and a clean, uncluttered design. The API was written in C++ for ease of programming. It has POSIX compatibility and access to a command line interface through the bash shell, although internally it is not a Unix-derived operating system.

BeOS was positioned as a platform which could be used by a substantial population of desktop users and a competitor to Microsoft Windows and Linux. However, it was ultimately unable to achieve a significant market share and proved commercially unviable for Be Inc. The company was acquired by Palm Inc. and today BeOS is mainly used and developed by a small population of enthusiasts.