Ivan Nemytchenko's proposed architectural building block for code that interacts with external systems (APIs, mailers, rest clients, Google Maps, Twitter). A manager isolates external-service calls from business operations so services stay procedural and focused. Injected dependencies belong on the manager, not the service — e.g. a message/rest-client pair is passed into the manager's constructor, not the method call. Complements mutators (for persistence) and stateless services (for business operations) in a layered Rails architecture.