The Tigase project's forums is based on the Drupal native forums functionality. Even though it doesn't have all the features of more advanced, dedicated forums tools like phpBB and others it served us well in last years and was selected for a number of reasons.
First of all I am still the only person maintaining the infrastructure for all the Tigase projects, that is the server itself, the website, shell/e-mail accounts, SVN repos, project tracking software and so on. Therefore the less software I have to look after the better for me. I selected Drupal because if offers quite a lot functionality in basic package, including forums. With thousands of modules available it can be easily extended with more stuff. So one of the reason to use Drupal built-in forums is the maintenance costs. Please note, new accounts registering functionality has been disabled because of a very high volume of spammers registering accounts and posting crap on the website.
Another reason is that I believe it is always better to have as much information as possible available in one place, so you don't have to search the whole web to find what you are looking for. My idea was to set up Drupal and provide all information related to the Tigase projects in one place: online documentation, blogs, articles, forums, new version releases and so on. This way we can even easily push the most interesting forum topic on the front page on the Tigase website.
Unfortunately the Drupal forums lack functionality which seems essential for some people. The main feature missing is integration with e-mail service. We offer XMPP notifications and we could potentially add a feature to submit comments and new forum topics via XMPP too but this seems not very convenient for some people. We can not, however offer mailing lists like functionality integrated with the Drupal forums. (I have never heard of such a module.) Having an extra mailing list to the forums is not an option at all. That would be very confusing and annoying to have 2 completely separate places for discussion. At least very annoying to me, as I am quite sure I would end-up with copying some topics between mailing list and forums.
However, as the Tigase community grows and changes I am open to any suggestions and I am willing to offer the community an opportunity to decide what way is the best. I have already received a few request to setup a mailing list. That would mean however, the existing forums is closed and we move all the discussions to the mailing list. Many others, however never complained so they are either happy with current system or they don't care enough.
To make sure we follow the community demands I will post a poll where everybody can vote and comment, sharing thoughts and preferences.