E-collaboration and collaborative systems bring geographically dispersed teams together, supporting communication, coordination and cooperation. In this paper we review forty-four products and research prototypes that offer collaborative services. The findings of our survey provide a list of the basic collaboration services, such as non real-time discussions, email, whiteboard, real-time discussions, screen sharing, file&document sharing and document management, and the examined products are presented with regards to those services. In sequence, they are classified to five functional categories, also defined taking into account the analysed features. In conclusion, important issues of collaborative computing are touched upon, and areas for improvement are identified.