twm, an initialism for Tab Window Manager, is a minimalistic window manager (WM) that is bundled with X Window System releases. twm is almost never seriously used for everyday use, but is often used as a fallback window manager in case something goes wrong with the default or is used until a more substantial WM can be retrieved. Being included with the ubiquitous X Window System itself, twm is not limited to use strictly on Linux or even *nix-like environments, but often follows X wherever it goes.
Development on it began in 1987 and the first stable release was made in April 1988. The effort was spearheaded by Tom LaStrange, a software architect employed by Solbourne Computer, Inc. in Longmont, Colorado, leading to it being unofficially known as "Tom's Window Manager" before the X Consortium took over the project in 1989 and subsequently changed the name to the one currently in use upon the release of X11R4. It served as the prototype for swm or the Solbourne Window Manager, a proprietary window manager which came pre-installed on all of the company's enterprise computing terminals beginning in 1990 and that introduced the concepts of virtual desktops and session management to the still nascent GUI ecosystem of the time.