1. Dependency Management: Apache Maven is a build automation tool known for its strong dependency management capabilities. It uses a declarative approach for managing dependencies through its Project Object Model (POM). On the other hand, Mill is a build tool that focuses on simplicity and speed. While it also supports dependency management, it uses a more flexible approach that allows developers to define dependencies using Scala code directly.
2. Build Configuration: Maven relies on XML-based configuration for defining the build process. It uses a predefined set of lifecycle phases and plugins to perform various build tasks. Mill, on the other hand, uses a Scala-based configuration DSL. It provides a concise and expressive way to define build tasks and dependencies.
3. Incremental Compilation: Maven does not have built-in support for incremental compilation. It typically recompiles the entire project even if only a small part of the code has changed. Mill, on the other hand, has built-in support for incremental compilation. It only recompiles the modified files, resulting in faster build times for larger projects.
4. Language Support: Maven is primarily used for Java projects and has strong support for Java libraries and frameworks. It also supports other JVM languages like Groovy and Scala. Mill, on the other hand, is specifically designed for Scala projects. It provides seamless integration with Scala and its ecosystem, making it a preferred choice for Scala developers.
5. Plugin Ecosystem: Maven has a large and mature plugin ecosystem, with thousands of plugins available for various build and deployment tasks. These plugins can be easily added to a Maven project using the POM configuration. Mill, on the other hand, has a relatively smaller plugin ecosystem. While it does have some plugins available, it may not have the same breadth as Maven.
6. Concurrency: Maven uses a single-threaded approach for executing build tasks. This means that the build process is executed sequentially, one task at a time. Mill, on the other hand, supports concurrent execution of build tasks. This allows for faster and more efficient builds, especially in multi-module projects.

In Summary, Apache Maven and Mill have key differences in terms of dependency management, build configuration, incremental compilation, language support, plugin ecosystem, and concurrency.