Out of Stock Notification

or search frequently asked questions:

Are out of stock notifications available for guest users?
Does this extension work with multiple options in one product?
Does this extension work with Color Swathes modules?
Can alerts subscription be disabled for certain products?
Can you only enable/disable stock alerts on a store-view level?
Are there any ready-to-use email templates for out-of-stock notifications?
I can't send notifications