SysLock

SysLock is a small utility that can lock your desktop so that no unauthorized user can access your computer while you are away.

Lock is triggered by clicking on the program icon; from that point on, access is only possible by entering the correct password. Keyboard shortcuts such as Alt+Tab or Ctrl+Alt+Del are also disabled at the time of locking. When locked, only the system wallpaper and possibly the password field are displayed.