1. A Computer-based system for prioritizing activities based on users access, comprising: an engine, including a processor, obtaining collections of resources as end user activities including, for each user, obtaining an activities access history of the user, the end-user activities including shared activities, a shared activity being an end-user activity having at least two end-users in common, the engine using respective feature vectors and generating a description of each shared activity with an individual user priority score taking into account differences in priorities among the at least two end-users of the shared activity, wherein each activity of the end-user activities of the obtained collections of resources contains resources and the engine records, for each said resource in the activity, access history of users, and wherein for a given shared activity, (i) the same feature vector is used to describe the shared activity and to calculate individual user priority score of the shared activity, and (ii) the respective obtained collection of resources providing a structure and membership of the given shared activity according to the individual user's last access to the shared activity, last update of the shared activity and connection strength between the individual user and other users associated with the shared activity; and an output module coupled to receive from the engine the shared activity descriptions and individual user priority scores, and outputs therefrom an activity list ordered by individual user priority, such that respective activity list of a user prioritizes collections of resources of that user, wherein the individual user priority scores are priorities for respective collections of resources of corresponding end-user activities and are based on properties of the corresponding end-user activities, the feature vectors enabling various metrics concerning the structure and membership of respective shared activity to be derived and utilized to calculate individual user priorities of the shared activity and thus respective collection of resources taking into account differences in priorities among the at least two end-users of the shared activity.