Whatsapp* has become the default†messaging tool for grassroots organising, whether it's party political canvassing, a local campaign or forming a tenants or workplace union. And Whatsapp works pretty well at the basics: you can be confident that your message is going to be delivered to everyone in your group, and because most people already have it, it's quite easy to start a new one and get people into it. But it's not adapted for the task of running an active democratic collective.
That's why I focus on building tools that work on Whatsapp, not because I like Meta particularly but because that's where people already are. Users are the most important part of any tool, because they can take it from a good idea to something that works really well.
Whatsapp isn't an open source technology and its API is quite expensive. There are tools that connect to it though, using the Whatsapp for Web websocket. That's how the Chat Hackers project that I lead connects our tools to Whatsapp. There's also the Baileys npm package for writing a quick Whatsapp tool.
If you want to build something using Whatsapp, I am very excited to help you.
* I recommend not using branded capitalisation for products
†This is starting to change to Signal in some communities, thank god