# Concepts

- [Inversion of Control](/release-1/concepts/index.md)
- [Castle Windsor](/release-1/concepts/index/windsor.md)
- [Autofac](/release-1/concepts/index/autofac.md)
- [Unity (v2 & v3)](/release-1/concepts/index/unity.md)
- [Puzzle Container](/release-1/concepts/index/puzzle.md)
- [Entities](/release-1/concepts/entities.md)
- [Property System](/release-1/concepts/entities/property-system.md)
- [Messaging and Message Broker](/release-1/concepts/message-broker.md)
- [POCO messages](/release-1/concepts/message-broker/poco-messages.md)
- [Standalone message handlers](/release-1/concepts/message-broker/abstract-message-handler.md)
- [Observers](/release-1/concepts/index-1.md)
- [PropertyObserver](/release-1/concepts/index-1/property-observer.md)
- [MementoObserver](/release-1/concepts/index-1/memento-observer.md)
- [BrokerObserver](/release-1/concepts/index-1/broker-observer.md)