# Concepts

- [Inversion of Control](/concepts/ioc.md)
- [Third party DI containers](/concepts/ioc/third-party.md)
- [Entities](/concepts/entities.md)
- [Property System](/concepts/entities/property-system.md)
- [Messaging and Message Broker](/concepts/message-broker.md)
- [POCO messages](/concepts/message-broker/poco-messages.md)
- [Standalone message handlers](/concepts/message-broker/abstract-message-handler.md)
- [Observers](/concepts/observers.md)
- [PropertyObserver](/concepts/observers/property-observer.md)
- [MementoObserver](/concepts/observers/memento-observer.md)
- [BrokerObserver](/concepts/observers/broker-observer.md)