Such an unusual domain name don’t you think? X.com is owned by Paypal and the domain is for their PayPal X Developer Network. This lets developers integrate PayPal payment processing services without forcing users to redirect to PayPal’s website to enter payment information.
This new initiative is designed to allow the company to better compete with the likes of Google and Amazon, which offer similar services. A great product from Paypal targeted specifically e-commerce sites.
Now, how much do you think Paypal paid for this domain? After all, common words made as domain are pretty expensive. This is actually the first time I have seen a 1 letter domain.