The Indian Railways online ticket system. Don't even think about queueing to buy a ticket, just go online and buy it there. It only has one major problem, you either need a local card or a AMEX... Otherwise it is a godsend, no endless Indian queues
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Agree that this is excellent - you can even print out your tickets in advance. And I used a Visa Credit Card from a British-based bank to buy tickets. I used the payment gateway on the site for Citi bank. Should be obvious when you get to that part of the system.
Is this your business?