Which APIs and SDKs Are Most Useful for Building Modern Messaging Apps?

Hi everyone,

I’m exploring messaging app development and I want to understand which APIs and SDKs are most effective for building modern, feature-rich messaging applications. I’m particularly interested in tools that can help with:

Real-time messaging and push notifications

End-to-end encryption and security

Media/file sharing (images, videos, documents)

Chatbots, AI-powered replies, or smart features

Cross-platform support (iOS, Android, web)

Scalability for large numbers of concurrent users

If anyone has experience with Firebase, Twilio, Sendbird, Stream, PubNub, or other messaging SDKs, I’d love to hear your thoughts on:

Ease of integration

Performance and reliability

Costs and licensing considerations

Any pitfalls or limitations to watch out for

Practical recommendations, examples, or open-source alternatives would be extremely helpful for anyone planning to build a modern messaging app.

Thanks in advance for sharing your insights!