NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is available for many platforms, including servers, desktops, handheld devices, and embedded systems.

The NetBSD project focuses on code clarity, careful design, and portability across many computer architectures. Its source code is publicly available and permissively licensed.

History
NetBSD was originally derived from the 4.3BSD-Reno release of the Berkeley Software Distribution from the Computer Systems Research Group of the University of California, Berkeley, via their Net/2 source code release and the 386BSD project. The NetBSD project began as a result of frustration within the 386BSD developer community with the pace and direction of the operating system's development. The four founders of the NetBSD project, Chris Demetriou, Theo de Raadt, Adam Glass, and Charles Hannum, felt that a more open development model would benefit the project: one centered on portable, clean, correct code. They aimed to produce a unified, multi-platform, production-quality, BSD-based operating system. The name "NetBSD" was chosen based on the importance and growth of networks such as the Internet at that time, and the distributed, collaborative nature of its development.

The NetBSD source code repository was established on 21 March 1993 and the first official release, NetBSD 0.8, was made on 19 April 1993. This was derived from 386BSD 0.1 plus the version 0.2.2 unofficial patchkit, with several programs from the Net/2 release missing from 386BSD re-integrated, and various other improvements. The first multi-platform release, NetBSD 1.0, was made in October 1994, and being updated with 4.4BSD-Lite sources, it was free of all legally encumbered 4.3BSD Net/2 code. Also in 1994, for disputed reasons, one of the founders, Theo de Raadt, was removed from the project. He later founded a new project, OpenBSD, from a forked version of NetBSD 1.0 near the end of 1995. In 1998, NetBSD 1.3 introduced the pkgsrc packages collection.

Until 2004, NetBSD 1.x releases were made at roughly annual intervals, with minor "patch" releases in between. From release 2.0 onwards, NetBSD uses semantic versioning, and each major NetBSD release corresponds to an incremented major version number, i.e. the major releases following 2.0 are 3.0, 4.0 and so on. The previous minor releases are now divided into two categories: x.y "stable" maintenance releases and x.y.z releases containing only security and critical fixes.