There are a number of ways to discuss API popularity. Our metrics are based on developer engagement. The "track" functionality on ProgrammableWeb lets developers declare an interest in receiving updates on particular APIs. Which APIs and categories are seeing the most activity.
Mastercard, a company that once warned that the risks of digital currency outweigh the benefits, has released two new blockchain APIs to promote collaboration and innovation in the digital exchange of value. Through its Mastercard Labs arm, Mastercard has indicated the API release is just the start.