Kotlin/Java (JVM) frameworks

Kotlin and Java, both running on the Java Virtual Machine (JVM), can use a wide range of frameworks due to their full interoperability. Some frameworks are primarily Java-based but offer excellent Kotlin support, while others are built from the ground up for Kotlin.

Here are some of the most popular and widely used JVM frameworks:

Enterprise & General-Purpose Frameworks

Spring Boot: The most popular framework in the JVM ecosystem, offering comprehensive support for building enterprise-grade applications and microservices. It provides concise APIs in Kotlin and seamlessly integrates the language's features like coroutines.
Quarkus: A cloud-native, full-stack framework designed for fast startup times and low memory usage, making it ideal for microservices and serverless functions in Kubernetes environments. It provides first-class support for Kotlin.
Micronaut: Another modern JVM framework built for cloud-native applications, featuring compile-time dependency injection to achieve fast startup and a low memory footprint. It works well with both Java and Kotlin.

Kotlin-Idiomatic & Lightweight Frameworks

Ktor: Developed by JetBrains, Ktor is a lightweight and flexible framework built entirely with Kotlin, designed for building asynchronous web applications and APIs using coroutines for high scalability.
Javalin: A minimalist and very lightweight web framework inspired by Express.js, ideal for simple REST APIs or smaller projects where simplicity and ease of use are key. It is designed with interoperability in mind, allowing applications to be built the same way in both Java and Kotlin.
http4k: A functional toolkit for Kotlin HTTP applications with a tiny footprint, based on the principle of "Your Server as a Function". It is written in pure Kotlin.
Vert.x: An event-driven toolkit for building reactive applications on the JVM. It offers dedicated support for Kotlin, making it suitable for real-time systems like chat servers.

Other Tools and Libraries

Exposed: A Kotlin-specific ORM (Object Relational Mapper) framework that provides a type-safe SQL-wrapping DSL and data access objects for database access.
Koin/Dagger: Dependency injection libraries. Koin is a lightweight, DSL-based DI framework built specifically for Kotlin, while Dagger is a popular Java DI framework that works seamlessly with Kotlin.
Kotest/JUnit: Testing frameworks. JUnit is the standard for Java, and Kotest is a Kotlin-native framework that supports various testing styles aligned with Kotlin's syntax.

The choice of framework often depends on project requirements. Large-scale enterprise applications typically leverage the robust ecosystem of Spring, while microservices or performance-critical systems might benefit from the lightweight, cloud-native properties of Quarkus, Micronaut, or Ktor.