In Unix computing, PWM is a lightweight X11 window manager, and the first to feature tabbed windows at the window manager level. The first version was released to the public in the spring 2000 under the Artistic License. PWM is no longer actively developed by itself, but has been superseded by Ion, by the same author, Tuomo Valkonen. The once unique tabbing feature has by now been reproduced in many new window managers, including KWin, Fluxbox, PekWM, wmii, and Ion.