Amazon Bitcoins was the first website to allow people to cash out their Bitcoin to buy Amazon Giftcards (2012-2013). All the user had to do was send Bitcoin to a generated address associated with their account, and they were emailed an Amazon giftcard for the equivalent amount of money.
I was the first person to integrate with Coinbase's API. I found a bug in it, and even helped their engineers fix it.
Ruby on Rails, API integrations, Bitcoin, Crypto