Building Collaborative systems with awareness (or groupware) is a very complex task. This article presents the use of the domain specific language CSSL v2.0 - Collaborative Software System Language -built as an extension of UML, using the metamodeling mechanism. CSSL provides simplicity, expressiveness and precision to model the main concepts of collaborative systems, especially collaborative processes, protocols and awareness.The CSSL concrete syntax is defined via a set of editors through which collaborative systems models are created. According to the MDD methodology, models are independent of the implementation platform and are formally prepared to be transformed. The target of the transformation is a web application that provides a set of basic functions that developers can refine to complete the development of the collaborative system. Finally, evaluation, validation and verification of the language is performed, determining that the CSSL tools allow developers to solve central aspects of collaborative systems implementation in a simple and reasonable way.