java 8 + lambda by any chance ?
we have been considering kotlin + vertx for some time now... so it would be interesting to hear about your experience in the vanilla java world.
Our core infra doesn't use lambda (we can't really, its not a good fit). However, I think for some of our ancillary services and especially for a lot of FlockOS apps (https://apps.flock.co), it makes a lot of sense.
Just yesterday in fact, I was at AWS dev day in Pune where I explained how easy it is to build a FlockOS app using lambda and node.js. We will put up a blog post on it soon.
Our backend is mostly Java, the desktop app is based on HTML/CSS/Javascript while the mobile apps are native.
We are working on a migration tool from Slack (and others) to Flock, we will release it soon.