Techniques for application activation are described herein. An operating system (OS) can be configured to incorporate various extension points that are serviceable through contracts defining individual invocations of extensible functionality. The extensible functionality is integrated as part of the OS and controlled by the OS in a centralized manner. However, the specific implementations of the extensible functionally are offloaded to applications using the contracts. For example, the OS can include or otherwise make use of a centralized application activation component that employs an object-oriented approach to invoke applications to perform particular contracts. The application activation component can pass information describing a particular contract to activate a designated application and enable the application to service the contract in the manner specified by the OS. In this way, the manner in which contracts are handled by application code can be managed and coordinated through a centralized application activation component.