I built the entire backend at first for 8 months before onboarding new engineers. I built it on GCP and Firebase. Had an extensive use of GCP products. Starting from Firebase (with all its products), to Cloud SQL (Postgres instance), BigQuery, AppEngine, Serverless cloud functions, PubSub, Recommendation engine, Cloud Logging.
External tools and APIs I used: Hubspot, SendGrid, Stripe, Aha (Jira like), Sentry, RapidAPI, Xero, Xirgo.