I'm author and maintainer of the Rep[lacement]Tags module (http://drupal.org/project/reptag). As mentioned and explained before the reptag module is a regexp-based, node-centric, bigger brother/sister of the Token module. The idea behind both modules is quite similar and even the API is similar on some points. For Drupal 6 I'd really love to see the modules complement each other (or even merge). To achieve that (at least for most of the features) only a few changes to Token and some more to Reptag ;) would be required.
Basically Reptag could provide two things to complement Token:
- The UI to manage tags (add/edit/remove) online from the admin pages
- A simple (yet powerful) plug-in system, so called .tags modules in reptag
I have posted a request to the issue queue a week ago which explains more details: http://drupal.org/node/141430#comment-619523
For a developers perspective on reptag's api you can read DEVELOPER.txt or try the module yourself to get an impression.
Regards Thilo