The Rules Autotag module takes a light-weight approach for autotagging full-text content by matching taxonomy terms (and optional Synonyms). Rules Autotag depends on the Rules module. Functionality is provided on different layers:
The API function rules_autotag_extract($text, $vocabulary) extracts terms from a given text which match a given vocabulary.
The basic rules action Extract terms (rules_autotag_extract_action) takes a text and a vocabulary as input and returns all matched terms.
The wrapper rules action set Autotag to terms list (rules_autotag_tag) directly stores the extracted terms into a terms list/field.
Comparison to related modules:
Taxonomy Autotagger takes a more user-oriented approach with by providing a AHAH-driven Autotag button.
Auto Tagging sends node content through any number of third party services to determine what the content is about.
A transport layer for Drupal-to-Drupal data, which aims to provide a common base on which to build services-based applications between Drupal sites.
In (reasonably) plain English:
with Services, you can make XMLRPC calls to a remote Drupal site and get back data, provided you first connect, log in, and pass keys and hashes and tokens and so on in ever call.
with Clients, you can just make a remote method call of, say, 'node.load' with a parameter of X and get back data, much like calling a normal function; all the complex stuff with Services is done for you.
with Transport, you need only say 'get me node X from Client Y', and you not only get the node, but the user who authored it, its attached files, taxonomy terms, and comments (well the last two are TODO, but that's a minor point). Transport does the work of calling the right methods, figuring out dependencies, saving everything it retrieves, and maintaining a record of correspondences between local and remote object IDs. Transport can work with multiple remote sites, and is agnostic of Drupal version: Transport on a Drupal 6 site can retrieve nodes from either a Drupal 5 or 6 site.
The Privatemsg Bulkmail module is intended for site administrators who want to send out an identical private message to a large user base (100.000 users and more).