- Airbnb built a new financial data pipeline called Braavos using Spark and Scala to replace their SQL-based system that could not scale with their growing data and complex accounting rules. - Braavos ingests platform and payment events and generates accounting entries through double-entry bookkeeping across subledgers like receivables, payables, revenue, and taxes. - It allows uniform processing of all products, querying of subledgers, and generation of normalized events which can be used to generate reports and recognize revenue according to financial policies. - The migration process involved generating historical events from existing data, building matching reports, testing with real events, and switching to the new system online.