This project provides TSLint rules that enforce immutability in TypeScript code by requiring the use of `readonly` modifiers, `ReadonlyArray`, and preventing mutation of arrays and objects. It also includes rules to promote functional programming style by disallowing `let` variables, `this` usage, classes, and certain statements like `if` and loops. The rules are designed for developers who want to ensure immutability and functional programming practices in their TypeScript applications, particularly useful in contexts like Redux/React where immutable state is important.