This is a list of interfaces or abstract classes in DD4T that are very commonly implemented cq. extended.

Interface	Rationale	Examples	Known customers	Priority	Notes
ILogger	Implement a different logging mechanism	Serilog, MEF	Essity, Ecclesiastical	High
IDependencyMapper	Add dependency mapping independently from any DI implementation	For custom DI implementations: read dependency mappings For any other customization: write dependency mappings	Essity, Ecclesiastical	Very High
DD4T ViewModel base attributes	See ViewModel base attributes for a complete overview	Various extensions to the ViewModel attributes	Fujitsu, Essity, Ricoh	High
ICacheAgent	Implement a different caching mechanism	Redis, serialized cache agent	Essity, Ecclesiastical	High
IPublicationResolver	Implement a custom publication resolving mechanism	Common practice is to create a publication resolver wrapped around the DynamicMappingsRetriever (which isn't out of the box in DD4T). Other use cases would be to use browser settings or Geolocation.	Many	Low	In Web 8 one could argue that the DynamicMappingsRetriever is always an improvement, and DXA 2.0 does not support older Tridion versions.

Overview of commonly used public classes / methods

This is a list of public classes and methods in DD4T that are very commonly used in customer implementations.

Class	Method	Rationale	Known customers	Priority	Notes
DD4T.DI.Autofac.Bootstrap	UseDD4T	Set DD4T default wiring	Many	Medium	If we rename this, it must be included in the release notes. Also note that any custom DI implementation also implements a method with the same name and signature.
DD4T.DI.Unity	UseDD4T	Set DD4T default wiring	Some	Medium	See above
DD4T.DI.Ninject	UseDD4T	Set DD4T default wiring	Some	Medium	See above
DD4T ViewModel attributes	See ViewModel Attributes for a complete overview	Support existing customer ViewModel classes	Many	Very high

Overview of common customizations