Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.

4chan - 4chan is a simple image-based bulletin board where anyone can post comments and share images.

Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.

Lainchan - Lainchan is a great imageboard package, actively building on it and adding a lot of features and...

Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.

Reddit - Reddit gives you the best of the internet in one place. Get a constantly updating feed of breaking news, fun stories, pics, memes, and videos just for you.