A new version of External Data, 0.7, has been released: I usually don't announce new releases on this list, but this is a major one, since External Data now supports retrieving data from two new sources: relational database, and LDAP servers. This excellent new functionality was contributed by David Macdonald.
This new access is handled by the new #get_db_data and #get_ldap_data functions, which can read from database tables and LDAP servers provided you've pre-configured them in LocalSettings.php; you can then display them in the same way as data retrieved from APIs. (Of course, there are privacy risks associated with both of these, and they should really only be enabled by people who know what they're doing.)
You can see more information here: