Design Patterns are commonly used in various applications to provide solutions for recurring design problems. Here are some popular design patterns used in software development: 1. Singleton Pattern: Ensures that only one instance of a class is created and provides a global point of access to it. 2. Factory Pattern: Provides an interface for creating objects, but allows subclasses to decide which class to instantiate. 3. Observer Pattern: Defines a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically. 4. Decorator Pattern: Allows behavior to be added to an object dynamically, without affecting the behavior of other objects from the same class. 5. Strategy Pattern: Defines a family of algorithms, encapsulates each one, and makes them interchangeable. This pattern allows algorithms to vary independently from clients that use them. 6. Adapter Pattern: Converts the interface of a class into another interface that clients expect. It allows classes with incompatible interfaces to work together. 7. Iterator Pattern: Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. 8. Builder Pattern: Separates the construction of a complex object from its representation, allowing the same construction process to create different representations. These design patterns, among others, are widely used in various applications to improve code organization, maintainability, and reusability.