Hack vs Self: What are the differences?

## Introduction
This Markdown code will provide key differences between Hack and Self, highlighting specific distinctions between the two programming languages.

1. **Language Type**: Hack is a statically typed language, meaning that variables must be explicitly declared and their types checked before runtime, while Self is a dynamically typed language where variables do not have predefined types and are checked during runtime.
   
2. **Inheritance**: Hack supports traditional inheritance where classes can inherit properties and methods from a parent class, while Self relies on a prototype-based inheritance model where objects inherit behavior from other objects.

3. **Memory Management**: Hack utilizes a garbage collector to automatically manage memory, while Self uses a technique called adaptive optimization that eliminates the overhead of garbage collection by optimizing memory usage dynamically.

4. **Concurrency**: Hack lacks built-in support for concurrency and relies on external libraries or modules for parallel processing, whereas Self offers intrinsic support for concurrency through the use of lightweight processes to execute tasks concurrently.

5. **Tooling and Ecosystem**: Hack has a well-developed ecosystem with support for popular development tools and libraries, making it easier to integrate into existing projects, while Self has a more limited tooling and ecosystem, which may require more development effort for integration.

6. **Community and Adoption**: Hack is backed by Facebook and has a large community of developers contributing to its growth and adoption, whereas Self has a smaller user base and community, leading to fewer resources and community-driven support.

In Summary, the key differences between Hack and Self lie in their type systems, inheritance models, memory management approaches, concurrency support, ecosystem maturity, and community adoption.