Elixir and Ruby differ in design philosophy, concurrency models, and performance. Elixir is built on the BEAM VM, enabling massive concurrency, while Ruby is more focused on developer happiness and simplicity.

Elixir and Ruby are both high-level programming languages, but they have distinct design philosophies and use cases. One of the primary differences lies in their concurrency models. Elixir is built on the BEAM virtual machine, which supports lightweight processes and enables massive concurrency. This makes Elixir particularly well-suited for applications that require real-time communication and high scalability, such as web servers or chat applications. In contrast, Ruby, while it can handle concurrency, primarily operates in a single-threaded manner, which can limit its ability to scale for highly concurrent applications. Additionally, Elixir emphasizes functional programming principles, encouraging immutability and pure functions, whereas Ruby is an object-oriented language that focuses on developer happiness and simplicity. Ruby's syntax is often seen as more approachable for beginners, while Elixir's syntax, though more expressive, may have a steeper learning curve. Performance-wise, Elixir typically offers better throughput in concurrent scenarios due to its lightweight process model. Ultimately, the choice between Elixir and Ruby often depends on the specific requirements of the project and the development team's expertise.