[<< wikibooks] Models and Theories in Human-Computer Interaction/Activity Theory through the use of tool: Wikibook
Activity Theory provides a method of understanding and evaluating a phenomenon, defining patterns and making inferences across interactions, describing phenomena and presenting phenomena through a built-in language and rhetoric.  A particular activity is a goal-directed or purposeful interaction of a subject with an object through the use of tools [1].  The wikibook is a perfect tool that provides the online collaborative platform to interact, share information and do research among the people from various locations.  It provides a mechanism, to bridge the gap between individual user and social reality around them.
Some people argue that the online collaboration is a second-best substitute for face-to-face communication.  However, it’s complement with its own perks and benefits.  In many circumstances, online collaborations, like most digital phenomena, is actually preferable to in-person collaboration.  Especially, when you are working with a virtual team, you can finish your work at end of the day and send your query or work product to a colleague in another time zone, and have an answer by the time you are back at your desk in next day morning.  Instead of waiting for the meeting or call that can address your question or provide that missing piece of information, you can reach out to a colleague with an instant message, email  or find an answer yourself by accessing an internal wikibook.
Citation: 
[1]  Fjeld, M., Lauche, K., Bichsel, M., Voorhorst, F., Krueger, H., Rauterberg, M. (2002): Physical and Virtual Tools: Activity Theory Applied to the Design of Groupware. In B. A. Nardi & D. F. Redmiles (eds.) A Special Issue of Computer Supported Cooperative Work (CSCW): Activity Theory and the Practice of Design, Volume 11 (1-2), pp. 153-180.