Geoshell is one of many Explorer.exe (the shell, not the browser) replacements available today for Windows. It takes the place of the current Start Menu, Task Manager, and Taskbar (including the Quicklaunch Bar and System Tray). Geoshell differs from other shell replacements in that it is expandable/upgradeable via plugins.
According to their website, Geoshell was designed to be light on resources. In fact, they claim it uses half the resources of the default Windows shell. It is said to be light and fast, making for a more responsive user interface.
See also:
litestep,
fluxbox