Skia

From midnite.liteman:

Skia is a window-hiding program. Applications that Skia has hidden will no longer be visible in the taskbar nor in Task Manager's Applications view. Skia uses the same low-level routines that your operating system itself uses to show and hide windows, so Skia operates quickly and stably. You can hide windows at the touch of a hotkey in any of three ways: you may hide the window under your mouse cursor, you may hide windows who have a window title that you specify, or you may hide all windows. If you wish, you may also disable CTRL+ALT+DEL and hide the system tray. Skia's control panel may be password-protected so that others may not un-hide your hidden programs.