MOO servers can be extended to include the information stored in other databases (MOO or otherwise) as well. A simple example of this is a dictionary tool that calls up a public-access dictionary on the Web, looks up the definition for a word, retrieves the result, and then presents this information to the user in the MOO.
A more complicated version of this same process can be found in AstroVR's ISSA postage-stamp server, which looks up images in an external database, and then presents them to the user. Other similar services provided by AstroVR include a postage-stamp server for the 2-micron all-sky survey (2MASS) and an interface to the NASA/IPAC extragalactic database (NED).
Dave Van Buren and Bill Drury developed a system for proposal reviews which stored and retrived information from an external SQL database (Sybase). Distributed object technologies such as CORBA could also be brought into play. In general, if it's network-accessible, the MOO can work with it.
Of particular interest are the possibilities for distributed virtual realities. Users could 'walk' from one world to another seamlessly. Supernova supports this invisible client re-direction already, making distributed worlds possible. However, there are many difficult high-level system issues (ranging from object transport mechanisms to security considerations) remain to be solved before a commercial-quality distributed MOO is feasible.