Public forums with ongoing discussions on Islam and its relationship to other religions are
but the latter of these might not be available at your site, (since not all news servers carry groups in the alt.* hierarchy).
Web access to newsgroups (search, read & post):
Before you jump into discussions it might be good to have a look at the charter for the Islamic newsgroup and the frequently asked questions on soc.religion.islam in regard to this newsgroup. Search the web to find the FAQs of other newsgroups.
For some newsreaders it seems to be difficult to post to the moderated newsgroups since the posts have to first go to the moderator email address. Hence, if you want to post to the Islamic newsgroup soc.religion.islam, send your contribution via email to email@example.com, firstname.lastname@example.org [using both makes it more certain that it arrives].
You might also want to have a look at the Christian newsgroups soc.religion.christian and soc.religion.christian.bible-study which discuss topics relevant to Christianity and other religions but the direct interaction with Islam is (sadly) relatively rare in these groups. FAQs are available for both soc.religion.christian and soc.religion.christian.bible-study.
The submission email address for soc.religion.christian is email@example.com and for soc.religion.christian.bible-study it is firstname.lastname@example.org
It is always good to think twice before hitting the deliver button and sending off a contribution to the newsgroups that will be read by thousands. But if you are having second thoughts, and urgently have to retract your contribution, here is the procedure how you might be able to undo it: CANCEL FAQ.
MCD has quite vigorous discussion by people who want to convince each other of truth. That makes it lively and interesting but sometimes it gets hot as well. If you would like to have a taste of what is discussed currently, have a look at the MCD Email archive.
subscribe bnai-avraham   email@example.com
SUBscribe ISLAM-L   your-full-name
This is not a religious debate list, but an academic forum (well, supposedly). Questions and statements allowed as far as they are relevant to the "History of Islam." ISLAM-L Web Archive
Note: I have never used chat rooms, this is the part of the discussion forums I am only semi-confident in recommending...
Answering Islam Home Page