A method, computer program product and system for detecting previously installed applications on a system. An installer program may invoke an application programming interface to call a software component, referred to as a “manager”, to detect previously installed applications on the system. The manager may be configured to query detection mechanisms, referred to as “collectors”, to perform their own detection techniques to detect applications installed on the system. Since each collector may perform its own unique detection technique, the collectors may be used together to detect more applications installed on the system than if the installer program attempted to detect the applications installed on the system by itself.