This category contains Unix-like systems designed for reduced hardware footprints such as legacy computers and embedded systems, not including systems that would have been state-of-the-art when the product was introduced (therefore leaving out ancient UNIX systems, for example, which are lightweight by modern standards).

Common features include minimal hardware and storage requirements, highly consolidated and space/memory-optimised userlands (using programs such as BusyBox or small API libraries), and removal of features such as preemptive multitasking that are not always supported by the hardware. This category also includes systems from the 1980s that ran primarily on microcomputers of that era rather than minicomputer or workstation-class systems.