In order to support our target group activity, i.e., meetings of non-collocated colleagues in different time zones, we need elements from the domains of real-time collaboration support, asynchronous groupware, and meeting capture and replay.
Supporting synchronous work
A number of tools provide awareness of the activities of other (remote) group members and enable real-time conversation and activity sharing, e.g., videoconferencing and desktop conferencing systems, media spaces, chat systems, and virtual spaces . The expense and overhead of videoconferencing generally limits use of such systems to infrequent, formally scheduled events. Desktop conferencing systems support more lightweight interactions, and feature text and/or audio (and occasionally video) for communication, mechanisms for awareness, and shared tools (e.g., whiteboards and text editors) for creating and manipulating artifacts.
Some desktop conferencing systems, such as TeamRooms  and its successor TeamWave , use a “place” metaphor (i.e., there are various rooms in which people meet, some designed for specific purposes, and the artifacts within those rooms are persistent across sessions). TeamRooms is primarily a text-based system, with graphic additions. Participants can communicate textually, share views of documents, and leave notes for one another. The latter is the only form of asynchronous communication. TeamWave provides the infrastructure for on-line interaction, supplemented with tools such as electronic whiteboards that mimic the tools collocated workers have at their disposal. In essence, TeamRooms tries to create a digital version of the traditional office with its opportunities and affordances for both formal and informal communication.
Other environments, such as the RoundTable product from ForeFront , use a meeting metaphor, and are geared specifically towards supporting formal meetings among distributed participants. In addition to text-based chat, participants may share images, documents, World Wide Web locations, audio, and video. Rather than gather together physically, each user connects to a server from his own office at an agreed upon time.
Providing a different twist on on-line meetings are systems such as DOLPHIN  and the Electronic Meeting Room (EMR) at the University of Hawaii, Manoa . These systems are based in physical meeting rooms, in which participants contribute via a keyboard and/or pen-based interface. Proponents claim that meetings are shorter because participants are able to work in parallel, and “talk” (type) simultaneously.
Chat systems and place-based virtual spaces known as MUDs (Multi-User Dimensions) and MOOs (MUDs Object-Oriented) were originally created for social purposes and games . In simple chat systems, users converse with one another by typing text. MOOs and MUDs also feature textual conversations, but these exchanges occur in a place-based context, and users can extend the space and create artifacts that define a particular place (e.g., creating virtual books and tables for a library room).
More recently, MUDs and MOOs such as The Palace  have become graphical spaces, augmenting text chat by the immensely popular use of avatars (a visual representation such as a graphic or photo of oneself) and other images or props. Still, the focus has remained primarily social. Notable exceptions are the Jupiter system from Xerox PARC , Jupiter's successor PlaceWare , and Electric Communities . Jupiter supplemented a text MOO with audio, video and interactive artifacts in order to make it a richer environment for professional work.
The popularity and sense of community created by these spaces suggest that some of their features (e.g., the place metaphor and the use of avatars) may be important elements in creating an inviting environment in which participants engage in collaborative work.
Excluding video-conferencing, all of these systems share some advantages in addition to just supporting communication between (possibly) non-collocated users. Because interaction takes place textually, it is simple to produce a written record of the proceedings. It is also possible for participants to remain anonymous if they wish. Finally, because these systems have a much lower overhead for participants versus traditional video-conferencing, they are practical for a variety of daily interactions.
These systems also share some shortcomings. Despite the claims of some desktop and video-conferencing systems, none of these technologies provides the broad spectrum of communication possible in face-to-face meetings. A key ingredient missing is the ability to transmit and sense cues such as turn-taking and acknowledgment of the floor that are often conveyed with body language and/or subtle facial expressions. These conventions are further hampered by the latency created by the input of textual utterances. Another drawback is in the maturity of the available tools to support work, e.g., shared editors, whiteboards, drawing tools, etc. Rarely do the tools provided in these systems approach the sophistication we readily find in their single user counterparts. Ideally, we would like to be able to incorporate the tools users are accustomed to having available on their desktop into these shared spaces. Finally, with the exception of leaving behind notes or other shared artifacts, these systems are still limited to synchronous interaction.
Supporting asynchronous group work
Because many kinds of workplace communication cannot be done synchronously, groupware and other tools for computer-supported cooperative work have been developed for supporting asynchronous workplace activities. Tools and suites such as Lotus Notes  provide strong support for asynchronous communication and coordination.
The most common tools for asynchronous communication are electronic mail, newsgroups, and groupware tools like Lotus notes. These tools not only allow a single user to dispatch information to a large number of people, but also support multi-user discussion such as brainstorming and other cooperative activity. Such systems preserve documents but do not often preserve the context in which those documents were created.
Both email and newsgroups create new documents at every communication; an extended discussion in either medium depends heavily on extensive quoting of earlier notes, to provide context for new additions. Other groupware tools focus on creating, updating, and sharing persistent documents. When co-workers collaborate asynchronously on a shared document, a coordination mechanism is needed to alert them to new work-related documents and versions, and to keep one user's updates from interfering with another's, whether they are made in disjoint or overlapping periods of time. Systems that do version control, such as RCS  for program source code, and Documentum  and DocuShare  for general documents, are common examples of coordination mechanisms. Other CSCW tools that manage documents may use a version-control system as part of their infrastructure, even if the end-user does not explicitly do version control operations.
More recently, asynchronous tools are incorporating features popular in synchronous tools, such as awareness, and integration of graphical media and audio and video. Awareness in particular is a valuable addition to synchronous collaboration, since awareness of co-workers increases the likelihood of collaborating with them . The Piazza System  embeds awareness of collaborators into artifacts themselves, with pictorial icons attached to document viewers, for example. While Piazza provides awareness of synchronous use, the idea of attaching awareness to artifacts was extended to asynchronous use in Timewarp , where the association of collaborators with the artifacts they have manipulated can be reviewed through an historical lens. Edwards and Mynatt describe the Timewarp system (which combines versioning and time-based browsing with asynchronous, coordinated resource sharing) as neither synchronous nor asynchronous collaboration; they call this hybrid model autonomous collaboration.
Replay. An emerging area in asynchronous computer-supported cooperative work is replay. Xerox PARC's meeting capture and salvage work  takes a real-time, synchronous meeting, captures the audio, the text recorded by a human note-taker, and drawings on the Tivoli  whiteboard, and saves them so that they can be revisited later. Any of the media can be replayed in coordination with the others. From a synchronous group activity, they produce a multi-media artifact that can later be reviewed, browsed, or studied asynchronously. Both PARC's WhereWereWe architecture  and work by Manohar  support this kind of multimedia replay.
Summary of requirements
To support virtual meetings between spatially and temporally separated colleagues, we require functionality drawn from the domains of real-time communication and collaboration, asynchronous groupware tools, and meeting capture. We require that our system be low-overhead to use, and that it support replay of the various media used in a meeting. In addition to straightforward replay, we need to be able to reconstruct decision-making processes and the context in which they occurred. This reconstruction should address the purpose of a meeting, namely to generate understanding of decisions, not just to present a list of items decided upon.
To apply the strengths of asynchronous collaborative tools to our virtual space, we must ensure that the tools that users ordinarily depend on to create and access persistent work documents are still available to them. The virtual space cannot effectively supplant these tools; instead, our goal is for the virtual space to coordinate other meeting documents. In common with real-time collaboration, we need the features of awareness and the ability to create and manipulate shared artifacts.
We hope that meetings in virtual space will share the benefits of other technology-mediated meetings, in promoting more equal participation by members .