The package comes with the following database modules:

dictorg
This module provides full support for the format designed by the DICT development group. This is a de facto standard for DICT databases. A number of dictionary databases in this format are provided by the the FreeDict project.
wordnet
Provides search capabilities for WordNet -- a lexical database for the English language, created and maintained at the Cognitive Science Laboratory of Princeton University.
gcide
Interface to GNU Collaborative International Dictionary of English.
outline
Support for databases in Emacs outline format. This module is designed mostly as an example and for testing purposes.
guile
It is an abstract layer for interfacing with database modules written in Guile. Such databases are, for example, operational on Runasimi.org and Ellinika.gnu.org.ua.
python
It is an abstract layer for interfacing with database modules written in Python.
mediawiki
This module allows to use Wiktionary or Wikipedia as a dictionary database. The Dicoweb page offers several databases defined this way.

The following modules provide additional lookup strategies:

stratall
A pseudo-strategy which returns all headwords, no matter what the search key was.
substr
This strategy matches arbitrary substrings anywhere in the headword.
word
Provides search strategies for matching separate words within headwords: word, first, and last. The word strategy matches a word anywhere in a headword. The first and last strategies match a word at the beginning or at the end of a keyword, correspondingly.
nprefix
Provides a variant of the prefix strategy which returns the specified range of matching headwords.
metaphone2
Implements strategy based on Double Metaphone phonetic encoding algorithm.
pcre
Use Perl-compatible regular expressions for headword lookup.

The following modules provide storage for user authentication databases:

ldap
An engine for using LDAP schemas to keep user authentication information.
pam
Implements user authentication via Pluggable Authentication Modules (PAM).