Abstract: Described are methods, systems, and apparatus for customizing applications based on user behavior data. User behavior data is collected and stored by an ad system based on a user's interactions. The user behavior data is associated with an ad system user ID. A request for first user customization data including an application user ID associated with a user device is sent by an application executing on a user device. The ad system user ID associated with the application user ID is determined by the ad system. User customization data is determined by the ad system based on the user behavior data stored by the ad system as associated with the ad system user ID. The user customization data is sent to the user device. A customization based on the user customization data is implemented by the application executing on the user device.

Abstract: A webpage comprising first instructions to request ID data from a first ad decision system on a second domain, and second instructions to request an ad from a first real-time bidding platform on a third domain is received, by a computing device, from a webserver on a first domain. The first instructions are executed, by the computing device, to send a first request to the first ad decision system, the request including first data stored on the computing device and associated with the second domain. The ID data comprising an ID are received, by the computing device, from the first ad decision system. The second instructions are executed, by the computing device, to send a request to the first real-time bidding platform for the ad, the request comprising the ID. The ad is received, by the computing device, from the first real-time bidding platform.