EpicMineTime

For players, just hold a sign in your hand, then right click a chest or any lockable block. If you want to lock a door, you may put a sign on the block above or below the door too. You may also SHIFT+RIGHT CLICK the block to prevent it get automatically locked, or you can write [Private] text manually on signs as well.

Share the chest with another user:
After claiming the chest, you can add another user on the sign. First, right click the sign, then enter /lock 3 <user name>

Share the chest with everyone:
Same as above, you just use [Everyone] (with brackets) in the username.

Add another sign:
If one sign is not enough, you may hold a sign and right click on another surface. It will snap on the surface and become a [More User] sign automatically. Placing the sign while holding SHIFT will bypass the sign creation.

Timer with doors:
I have no idea why Lockette is doing this, but I am adding this feature anyways. If you add a line [timer:X] (with brackets, and X means an integer) to a door lock, the door will automatically close after X seconds.