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.
exchangeratesapi.io - Foreign exchange rates API with currency conversion.
ExchangeRate-API - An easy to use, free & reliable Exchange Rate API trusted by tens of thousands of developers since 2010!
Open Exchange Rates - Free, hourly-updated exchange rates - a simple, accurate, open-source JSON API. Free for personal use, a bargain for everybody else.
BestExchangeRates - Compare FX and save when you send or spend abroad
Kantox - Kantox is a fintech company offering FX management solutions.