Virtual worlds: By far the most prominent virtual world is Second Life ⁵⁴ (though others such as There.com exist too). What sets it apart from online role-playing games like World of Warcraft (which are orders of magnitude more popular) are the facts that they do not have predefined storylines or goals and that they give their users freedom to create and use almost whatever objects they choose, possibly making money in the process. In this sense, they represent a genuine alternative to the real world. Pedants might argue that Second Life is not really a Web 2.0 service because it is not technically part of the web (i.e., it does not use HTML and HTTP, though it can interact with the web in various ways). But at a more abstract level, the participative, user-generated environments that have grown inside Second Life are as good examples as exist anywhere of the 'architecture of participation' principle. The greatest scientific potential seems to lie in education and in conferences. Second Life provides an environment in which people from different locations can come together quickly and easily into a shared space that to some extent mimics the real world in important aspects of human communication such as physical proximity, gesture and the ability to seamlessly mix one-to-many with one-to-one communication (e.g., chatting to the person beside you during a lecture). As a result, educators have poured in – around 160 universities now have a presence in Second Life ⁵⁵ – as have some scientists. There is even a continent called the SciLands where a number of groups with scientific interests have congregated (though from a distance, and to my eyes, its administration appears dauntingly bureaucratic). Nature Publishing Group also has it's own small archipelago – inevitably called Second Nature and consisting (at the time of this writing) of three separate islands – on which a diverse group of scientists is building and maintaining educational features in evolutionary biology, genetics, cell biology, chemistry and earth sciences, among others. There are also meeting, presentation and poster display areas. The degree of activity and enthusiasm has, quite frankly, astonished us. True, Second Life and other virtual worlds are still at an early stage in their evolution, are clunky to use, and require large doses of patience and practice to get the most out of them. But the same was true of the web during the early 1990s and look what happened there. One major factor working against Second Life's rapid expansion is the fact that it is a proprietary 'walled garden' controlled by a single commercial organisation, Linden Lab. In this sense, it is more like early AOL than the early web. But conversations with staff at Linden Lab suggest that they understand this potential pitfall, and they have already released, as open source, the code to their client application.⁵⁶ If the server side code is opened up too, then the eventual results could be as momentous and world-changing as the web itself.

One class of social software that deserves special comment is social bookmarking tools.⁵⁷ One of the earliest was del.icio.us,⁵⁸ and its introduction of tagging – freeform keywords entered by users to facilitate later retrieval – soon gave rise to the concept of the 'folksonomy,' ⁵⁹ a kind of implicit collective taxonomy or ontology generated by the aggregate, uncoordinated activity of many people tagging the same resources. Some commentators, notably Clay Shirky ⁶⁰ and David Weinberger,⁶¹ have argued (convincingly in my opinion) that this approach, although anarchic, has certain advantages over traditional centralized taxonomic approaches (such as the Dewey Decimal System). In particular, traditional approaches have difficulty dealing with entities that belong in multiple categories (is Nature a magazine or a journal?), or about which our view changes over time (Watson & Crick's 1953 paper reporting the structure of DNA is in the field of biotechnology, but that word did not exist at the time). Since such challenges are often particularly acute in science, which necessarily operates at the frontiers of human knowledge, it is tempting to wonder whether collaborative tagging can help in that domain too.⁶²

Nature Publishing Group has its own social bookmarking and reference management tool, Connotea,⁶³ heavily inspired by del.icio.us but with certain features added with academic researchers in mind. As well as providing a way for researchers to store, organise and share their reading lists, we were also interested to find out how useful the resultant collective tag metadata could be in helping to automatically link together related online scientific resources. To that end, we developed code for the EPrints institutional repository software ⁶⁴ that enabled it to query Connotea for tag information and automatically derived related reading suggestions. The experiment proved a success ⁶⁵ and we have built tagging into many of the applications we have developed since then (e.g., Nature Network, Nature Precedings and Scintilla) with a view to implementing similar features when the data sets grow large enough.