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!
Makerlog - Makerlog is the dead-simple task log that helps you stay productive and ship faster.
exchangeratesapi.io - Foreign exchange rates API with currency conversion.
WIP.co - Work in progress. We are a community of makers who help each other ship product.
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.
Indie Hackers - Connect with fellow entrepreneurs, developers, and bootstrappers who are sharing the strategies and revenue numbers behind their companies.
Open Exchange Rates - Free, hourly-updated exchange rates - a simple, accurate, open-source JSON API. Free for personal use, a bargain for everybody else.