For fun and exercise, to practice pair programming and TDD, our team has built a web application from scratch in Kotlin, including all necessary parts (web server, database, framework), all in one. The only production dependency is the standard library. https://github.com/7ep/r3z . Perhaps you will find it useful. Let me know.

It looks very good. One very minor and random observation: I notice your team puts all your exception classes in folders called "exceptions". This is quite a common practice, but I'm not convinced that it's the best practice. Exceptions conventionally have names ending in "Exception", so there's no need to give them another namespace: there's no risk of name clashes with non-exception classes. Instead, exceptions could be in the same package as the classes that use them: placed according to the domain they relate to, not according to the fact they're exceptions.