In general, gradle seems like the thing that most people are using. Using alternate build systems might of course work but especially with kmm you are pretty much on your own when stuff doesn't work. I'd recommend against maven for the same reason. It might work and if it does, good for you. But if it doesn't, you'll be figuring a lot of stuff the hard way. And kmm is of course a bit less mainstream then some of the other stuff in kotlin. So, there's that.