Computer mediated communication is the main research focus and the most used form of CSCW (Baecker, 1993; Keisler, 1997). Email and bulletin boards are the simplest and yet most successful asynchronous CSCW systems (although there are synchronous variations). The growth of distributed organisations has been attributed, in part, to email as an effective form of computer mediated communication. This communication medium has led to the emergence of on-line communities with their own specific HCI and social interaction problems e.g. information overload, lack of recipient feedback, inappropriate informality etc.

The history of videoconferencing has developed in parallel with advances in the technology (Baecker, 1993). Listing them in chronological order multimedia communication started first with close-caption TV (CCTV) with dedicated lines transmitting (synchronous) video directly to participants. Video conferencing began with the transmission of group images from one room to another via a common monitor. Multimedia communication really came into its own with the advent of desktop videoconferencing. Users sit in front of their computer and communicate in real time (synchronously) via a microphone, camera and (often) a digital workspace. This configuration is often referred to as a picture-in-a-picture (PIP) setup or CuSeeMe. The communication can take place on a point-to point basis or can involve many individuals and sites.

With the introduction of media spaces, distributed users access one another, like videoconferencing systems, via video and audio links. However, media spaces not only support explicit, intentional interactions and shared artefacts but also informal interactions and awareness. These informal communications (colleague presence, activity and availability awareness, and unplanned interactions) have been identified as critical to effective group work. Awareness technologies have evolved to allow distributed workers awareness of their co-workers and of their potential for collaboration. These technologies invariably use video images as the main data source for awareness although there are audio only awareness tools.

Internet-based videoconferencing has been regularly used since the early 1990’s . However, the first major enhancement to Internet videoconferencing has been the advent of multicasting. A Unicast connection transmits data on a point-to-point basis whilst a Multicast connection allows for data to be transmitted to multiple recipients. During multicasting the network replicates (at the routers) the packets transmitted. The replicated packets can be sent to as many recipients as have requested the data and are members of the multicast group. In multicast conferencing, audio and video are sent in different streams. Desktop conferencing facilities on computer workstations, can use a combination of multicast conferencing tools.

Virtual reality is a computer-based application which allows human-computer and human-human interactivity through a sensory environment called the virtual world which is dynamically controlled by the user’s actions. Virtual environments rely heavily on the notion of immersion both physically and cognitively. Keyboard and monitor input devices allow a user to be partially immersed whilst head mounted displays produce total-immersion in the environment. A user is cognitively immersed in the environment when they feel immersed in the action.

Collaborative virtual environments provide remotely located users with the ability to collaborate via real interactions in a shared artificial environment. Virtual reality communication environments have been argued to provide a natural, intuitive environment for communication with the added benefit of removing some of the social taboos from social interactions. Virtual reality animated actors called avatars aid the user in their interaction with others in the virtual reality environment making it seem more natural in two ways. Firstly, avatars can represent the user within the environment - a user relates and collaborates with other users via their avatars. Secondly, an avatar can represent a software agent with the actor’s behaviour defined by that agent.

Meeting support applications and tools have emerged as a form of support for local synchronous meetings rather than with computer mediated communication, which has traditionally been primarily a support for remote synchronous & asynchronous collaborations (Preece, 1995; Keisler, 1997; Dix, 1998).

Meeting room systems often take the form of a meeting room furnished with a large screen video projector and a number of computer workstation / terminals.

Most of these systems focus on improving decision-making by groups rather than individuals. The large screen and all the participants’ screens show the same image and this tool is often used as an electronic whiteboard easily accessible by all the group members.

Argumentation tools support and document multiparty arguments and negotiations. Many argumentation tools have been developed to support system designers in the decision making process. Tools that support argumentation often have a hypertext type format which allows designers to work simultaneously (synchronously) although they are often used asynchronously by local group members.

The aim of co-authoring systems is to support the collaboration necessary between co-authors in producing a document. The general mode of interaction for these systems is asynchronous cooperation with each user working as a semi-autonomous individual on a portion of the document. Many of these systems use a hypertext model. The text forms the basis of the interaction with linked networks of data (usually text or graphics) connected to this basic structure. Shared editors, in contrast to co-authoring systems, work synchronously with text or graphics. Specific problems occur with this synchronous mode of interaction.

Shared diaries and calendars are often used for CSCW purposes. This idea has been taken further with active badges which track the whereabouts of users within a building and then relay the information back to a shared diary system. The accessibility of the resultant information has many social impacts that are becoming more evident especially with reference to privacy issues (see the next section)

Shared workspaces and window systems are examples of synchronous collaboration applications.

An important aspect of these shared applications is the notion of floor control – who has control over the application at any one time. There is either a social protocol in force or technical mechanisms imposed by the system which work on a first-come / first-served or turn-taking basis.