Ion is a tiling (no overlapping windows) window manager that also has PWM-style tabbed frames which can contain multiple client windows.

PWM is a lightweight x window manager that can have multiple client windows attached to a single frame, that can be switched between via tabbing. The author of PWM, Tuomo Valkonen, has ceased development on PWM and now works on PWM’s successor: Ion. Although PWM is now no longer being actively developed, PWM’s tabbed windowing feature has been extremely influential and many other window managers have copied it. External Links PWM FAQ

Fluxbox is a lightweight and highly configurable window manager with pwm-like tabs, based on the Blackbox window manager.