amigaworld.net used to be one. At first it was derided and "boycotted"* outside of the OS4 community, then when it turned out to be really popular, people tried (successfully) to make it more inclusive. So then amigans.net was started, which appears to now be in phase 1 of the same cycle...
*Was pretty funny seeing people with no interest in OS4 claiming to boycott a site that wasn't trying to cater for them anyway...