Can you develop your own messaging system in your Apps or Websites?

Yes, you can develop your own messaging system in your apps or website. Messaging System like WhatsApp or Slack which support text messages, media messages, voice & video calling and many more features using these platform.

Add voice, video, text chat to your apps and websites
CometChat enables developers to integrate customizable chat in their own apps and website. Also, it is cheaper as compared to other platforms.
We suggest that developers or start-up can use them as it helps them to save their time and budget.
Links: Dashboard, Documentation, Github

Propel user engagement retention, and conversion with chat.
SendBird provides an easy-to-use Chat API, native Chat SDKs, and a fully-managed chat platform. It provides a large set of features as compared to other platforms but also expensive for developers to use. An enterprise, well-funded start-ups, or corporates looking for large sets of features can use them.
Links: Dashboard, Documentation, Github

PubNub APIs & SDKs Help to Quickly Implement Secure, Collaborative Features in Chat Apps.
PubNub is a communication platform which helps developer to easily integrate real-time communication system in their apps. Apart from real-time chat it also provides Geo-Location, IoT services that help developers to cover a large set of usecases. Its plan is cheaper as compared to other platforms.
Free Plan provides 200 MAU with all the chat-related features. So at the initial phase, if you are looking to chat on your app or website. It’s good.
Links: Dashboard, Documentation, Github