1. Syntax and Expressiveness: Ruby is well-known for its expressive and elegant syntax, which allows developers to write code that is easy to read and understand. It has a concise and flexible syntax that enables developers to write code that looks like natural language. Go, on the other hand, focuses on simplicity and readability. It has a more strict and minimalistic syntax that makes the code easy to write and maintain. Rust also has a fairly strict syntax, which aims to prevent common programming errors and promote safe code.

2. Concurrency and Multithreading: Go has built-in support for concurrent programming, which allows developers to write efficient and scalable concurrent programs. It has goroutines and channels that simplify the handling of concurrent tasks. Ruby, on the other hand, has a Global Interpreter Lock (GIL) that restricts true parallelism and limits the effectiveness of multithreading. Rust provides low-level control over threads and has features like ownership and borrowing that guarantee memory safety even in a multithreaded environment.

3. Runtime Performance: Go is designed to be a fast and efficient language, with a focus on high-performance applications. It has a garbage collector that manages memory automatically and reduces the risk of memory leaks. Ruby, being an interpreted language, is generally slower than Go, but it compensates for it with its simplicity and productivity. Rust, being a systems programming language, focuses on providing high performance and control over system resources. It compiles to native code, and its zero-cost abstractions result in efficient execution.

4. Memory Safety and Error Handling: Rust is known for its focus on memory safety. It enforces strict compile-time checks to prevent common programming errors like null pointer dereferencing and memory leaks. It also provides an alternative to exceptions called "Result" which enforces proper error handling. Go, while not as strict as Rust, also provides memory safety through its strong typing and garbage collector. Ruby, being a dynamically-typed language, is not as strict when it comes to memory safety.

5. Community and Ecosystem: Ruby has a large and vibrant community that has created a rich ecosystem of libraries and frameworks. It is widely used in web development and has popular frameworks like Ruby on Rails. Go, although relatively newer compared to Ruby, has a growing community and a good number of libraries and frameworks. It is known for its simplicity and is often used in backend and distributed systems development. Rust has a smaller but highly active community. It is gaining popularity in areas like system programming, game development, and embedded systems.

6. Learning Curve and Documentation: Ruby is considered to have a relatively easy learning curve due to its expressive syntax and friendly community. It has extensive documentation and many resources available for beginners. Go also has a relatively easy learning curve, thanks to its simplicity and readability. The Go team has invested a lot in providing good documentation and resources for beginners. Rust, on the other hand, has a steeper learning curve due to its focus on memory safety and ownership. However, it has an excellent official documentation and a supportive community that helps beginners learn the language effectively.

In Summary, Go, Ruby, and Rust differ in their syntax, concurrency support, runtime performance, memory safety, community, and learning curve. Go focuses on simplicity and concurrency, Ruby on expressive syntax and flexibility, and Rust on memory safety and performance.