In this paper we introduce Virtus, a web-based platform that provides enhanced functionalities to automate the management of users, groups and virtual communities using an expert rule-based system. Virtus supports collaborative learning using a group contract by automating the execution of the rules of the contract. The originality of our work consists, on the one hand, in proposing a declarative language to express contracts using declarative rules, commitments and role responsibilities assigned to members of a group or participants of a community and, on the other hand, in automatically executing the contract, implemented by an expert system. Once the contract is defined, it is translated into an executable rule language. Periodically, Virtus platform extracts information from the virtual environment and activates a knowledge-based system for each group.