Woot! is not just an exclamation of joy but is also a shopping site. Each day a single item is offered for sale at an unbelievably low price. The item is then offered until all available stock has been sold or the 24-hour period is up. However, I have rarely seen an item make it past midday.
As they say in their FAQ:

I see only one item, do you sell anything else?

No. We sell one item per day until it is sold out or until 11:59pm central time when it is replaced (see next entry for details). However, each item we sell is in stock and typically ships within 2-3 business days.

So the key is to shop often.