1. Architecture: Amber Framework is built on Crystal, a statically-typed language with a focus on performance and safety. This can result in faster execution speeds and better memory management compared to Ruby on Rails, which is built on Ruby, an interpreted language.

2. Community Support: Rails has been around longer and has a larger community, resulting in more resources, plugins, and tutorials readily available. While Amber Framework may have a smaller community, it can benefit from the Crystal community's support and expertise.

3. Conciseness: Amber Framework is known for its concise syntax and built-in functionalities, making it a lightweight and efficient choice for web development. In contrast, Rails can sometimes be criticized for being too verbose due to its convention over configuration approach.

4. Learning Curve: Due to its simplicity and lightweight design, Amber Framework can have a shorter learning curve for developers who are familiar with Crystal or similar languages. On the other hand, Rails' extensive features and conventions may require more time to master for beginners.

5. Performance: Amber Framework's performance is often highlighted as a key difference from Rails, as it leverages the speed and efficiency of the Crystal language for high-performance web applications. This can be particularly advantageous for applications with intense computation or high traffic.

6. Flexibility: Rails is known for its flexibility and ability to handle a wide range of web development tasks, thanks to its extensive ecosystem of gems and plugins. While Amber Framework may not have as many options available, its focused approach can lead to better performance and streamlined development.

In Summary, the key differences between Amber Framework and Rails lie in their architecture, community support, conciseness, learning curve, performance, and flexibility.