Our API directory now includes 46 bitcoin APIs. The newest is the Btc.to API. The most popular, in terms of page visits, is the BitStamp API. Below you'll find some more stats from the directory, including the entire list of bitcoin APIs.
Airbitz has utilized its Bitcoin Wallet Plugin API internally and through select partners for a while. Now, the company has released the API to its entire user base. Airbitz expects the API to boost cryptocurrency usage through integrations with everything from marketplaces to gift card vendors.