The only forum that does not curtail “freedom of speech” or the right of people to assemble peaceably, nor does it prohibit the free exercise of religion.
Discussions concerned with what is the correct way to educate a person (e.g., Locke's Thoughts Concerning Education).
Discussions concerned with the philosophical study of history, particularly concerned with the question whether history (i.e. the universe and/or humankind) is progressing towards a specific end?
Discussions concerned with how our languages affect our thought(s).
Discussions concerning the study of government and nations, particularly how they came about, what makes good governments, what obligations citizens have towards their government, and so on.
Discussions concerning attempts to ascertain exactly what the mind is, how it interacts with our body, do other minds exist, how does it work, and so on. Can be expanded to include issues of AI.
Discussions geared toward philosophical thinking that is inspired and directed by a particular religion. It can be done objectively, but may also be done as a persuasion tool by believers in that faith.
Discussions concerned with whether scientific knowledge can be said to be certain, how we obtain it, can science really explain everything, does causation really exist, can every event in the universe be described in terms of physics and so on.
Secular beliefs. Discussions denoting attitudes, activities, or other things that have no religious or spiritual basis.