Logging Services - logging abstractions and implementations for common scenarios and logging frameworks.
Castle DynamicProxy - a lightweight, lightning fast framework for generating proxies on the fly, used extensively by multiple projects within Castle (Windsor) and outside of it (Moq, NSubstitute, FakeItEasy, Rhino Mocks).
Castle DictionaryAdapter - on the fly generates strongly typed wrappers around untyped dictionaries, or chunks of XML (like config file), optionally adding support for change notification, cancelation, error notification and other features.