10 realtime data sources you won't believe are free!

This blog discusses various realtime data APIs that can be used to build an app. The sources are divided into transport, weather, and currency categories. For transport data, Helsinki Transit Data, TfL Open Data, Kystverket, and FlightRadar24 are mentioned. Weather data sources include Open Weather Map and Weather API. Currency data can be obtained from Exchange Rate, PredictIt, Binance, and Coinranking. Tools such as Postman, AsyncAPI, and Ably Labs Ingester are recommended for testing and defining WebSocket APIs. The blog also provides information on how to get started with these APIs using Ably's platform.