Design Patterns in Magento 2:
Following design patters is the key factor in magento 2.x
1. MVVM Pattern
2. Singleton Patter
3. Dependency Injection Pattern (di files)
4. Abstract Factory pattern
5. Factory Method pattern.
6. Event Observer Pattern (Event & Observer concept)
7. Object Manager Pattern
8. Proxy Pattern
9. Composition Pattern
10. Builder Pattern
11. Adapter Pattern
12. etc