An online system provides a user with access to applications associated with third parry systems via the online system and generates an identifier that identifies the user to a third party system without providing the third party system with information personally identifying the user. Using an identifier that identifies an additional user to the third party system, an online system user may invite the additional user to use an application associated with the third party system without installing the application on the additional user's client device. When the user invites the additional user to use the application, the online system sends the third party system associated with the application the identifier identifying the additional user to the third party system. If the additional user accepts the invitation, the online system or third party system provides application content to the additional user via a frame on the additional user's client device.