Stellar is a recently released protocol for creating a distributed exchange. It provides a simple way for anyone to become a "Gateway" into the network, by issuing their own credits. For example, friends can be "Gateways" for each other since they have mutual trust and are willing hold debts for each other.
The problem is that right now there are only 2 Stellar gateways, and there's no use in using a "distributed" exchange with only two entrances and exits.
Astral is a proof of concept service that gives any website the ability to become a Stellar gateway, with the added benefit of providing a gift card program. The website integrates the service into their checkout flow and can then sell gift cards, injecting their credits into the Stellar network. Those credits can then be traded and eventually used at the website again to purchase goods.
Not only is this vital for the Stellar network, it also allows the website to accept effectively any currency through the Stellar exchange.