With the launch of the KaiOS Developer Portal, developers new to the platform have all of the tools they need to begin building and distributing apps for KaiOS. The guide can help you get a feel for things with sample code, there are instructions for setting up your development environment, and there’s an easy to set up simulator that lets you run your app virtually to ensure everything is working.
KaiOS is used by more than 100 million people, so there’s definitely value in taking a look if you’re a mobile developer.