Usually, if you don’t want anybody else to use your computer while you are away from your desk, you lock it (Win+L). But if you need to lend your computer to another user but don’t want them to access certain running applications like your email program or calendar application, you will need to use LockThis!.
LockThis! is a tiny Windows utility that makes it possible to password protect almost any programs or documents that's currently running or minimized.
When LockThis! is running a small lock icon is visible on the system tray. The program gets activated on first run and the admin panel is password protected by default. Enter the default password (LockThis!) to unlock the admin panel where you can change your password and a few other settings.
To lock any application just press the CTRL button when minimizing a window. This will prompt you to supply a password for the minimized window. You can either choose to use the same admin password for each application, in which case you won’t be prompted for a password, or choose to use different passwords for different windows. Once the password is supplied, the minimized window gets locked and a graphic is displayed briefly in the middle of the screen indicating the success of the process.
If you try to restore the minimized application you will be prompted once again for the password. The window cannot be restored until you enter the correct password.
LockThis! is free and works with Windows XP, Vista and 7.