SmallWindows is described as 'Exposè (now Mission Control ) functionality on Windows was a bit tricky to develop, but SmallWindows is somewhat successful at it. However, you'll see plenty of glitches during day-to-day use' and is an app in the OS & Utilities category. There are eight alternatives to SmallWindows for Windows, Linux, Mac and BSD. The best alternative is KWin, which is both free and Open Source. Other great apps like SmallWindows are Mission Control (Paid), Raskin (Free), Topdesk (Paid) and Winflip (Free).
KWin is a window manager for the X Window System, and is in the process of becoming a Wayland compositor. It is an integral part, and the default window manager of the Plasma Workspaces, but it can also be used on its own or with other desktop environments.
Sawfish is an extensible window manager using a Lisp-based scripting language. Its policy is very minimal compared to most window managers. Its aim is simply to manage windows in the most flexible and attractive manner possible.