These are some sites which are either ran by Heyuri users or mutually linked with Heyuri:

Japanese BBS Directory: An English-language directory of Japanese BBSes
Wirechan: A Lain focused community that encourages philosophical, esoteric, alternative, counterculture related, technological and cyberpunk discussion, this being with a mature userbase
✝ Ayashii World@Shinkai 10000: An underground Japanese Ayashii World instance
Muscle Babes Directory: A global guide featuring female bodybuilders, amazons and fitness models
BJDgallery@Arcesia: An image booru of ball-jointed dolls
✝ Nashikouen: A SFW imageboard for all ages
アダルト画像掲示板.COM: A list of Japanese adult imageboards
投稿画像の壷: A list of Japanese adult imageboards and blogs
✝ Rotting Angels of the Omnipotent Eye: An imageboard/forum hybrid
萌えらんくBEST100: A list of Japanese moe sites.
20chan: A friendly imageboard whose admin is a Heyuri user

If you are interested in mutually linking your website with Heyuri, please make a thread on Site Discussion instead of privately e-mailing me.