For https://ably.io (Ably Realtime)
- Stripe (payments)
- PipeDrive & Intercom (CRM integration)
- Zapier (some automation between systems)
- Rollbar & Sentry (error tracking)
- AWS S3 (file storage)
- AWS Route53 & CloudFlare (DNS)
- AWS EC2 APIs (Infrastructure provisioning)
- AddSearch (search)
- Freshdesk (tickets)
- Sendgrid (email)
- Google Recaptha (captcha)
- APILayer (tax)
- Monitis & Uptrends (monitoring)
- Browserstack (browser automation)
We use 100s of services (https://blog.ably.io/94-tools-you-need-to-grow-your-startup-...), but I've only listed the key services where we integrate with their APIs.