ExchangeRate-API.com offers an easy-to-use JSON currency conversion API with unlimited free requests. The service supports all 160 major currency codes and an incredibly accessible API request format. ExchangeRate-API has been a popular option for developers to get exchange rate data since 2010!
LearnVest - Make progress on your money.
Fixer.io - Fixer provides a free, simple, and lightweight API for current and historical foreign exchange rates and currency conversion. The API tracks rates published daily by the European Central Bank.
CalendarBudget - The easiest way to track and forecast your wealth - using a calendar.
exchangeratesapi.io - Foreign exchange rates API with currency conversion.
Merrill Edge - Merrill Edge is a brokerage platform that helps in investing, provides advisory consultations, and other services.
Open Exchange Rates - Free, hourly-updated exchange rates - a simple, accurate, open-source JSON API. Free for personal use, a bargain for everybody else.