Comparison of Glossary-type modules (currently just Glossary and G2) : http://drupal.org/node/266511
Quote from Glossify's project page:
"This module ( glossify ) is similar to Glossary (taxonomy term-based, usage ~1400 as of May 2009) and G2 Glossary ( node-based, usage ~20) modules."
Here is the issue in glossify's queue that we together with Sun will use to log our efforts in module consolidation - http://drupal.org/node/500218.
This is a difficult category to describe but it's easy to see that the following modules fulfill the same basic need.
Keyword Link
http://drupal.org/project/keyword_link
Active Taxonomy Links
http://drupal.org/project/active_taxonomy_links
Alinks
http://drupal.org/project/alinks
Glossary
http://drupal.org/project/glossary
G2 Glossary
http://drupal.org/project/g2
Glossify Node Interlink
http://drupal.org/project/glossify