Unity chan comes to mind but I think they are not common.
Exerpt from chans license agreement…NO NUDE LEWD CHAN.
3.2 With respect to the use under the foregoing paragraph, Users shall abide by all terms of use in the following items:(1) Having this License be succeeded to third parties who receives the Distribution, etc. in case of Distributing etc. the Company’s Characters and its Derivative Works;(2) Not using the Company’s Characters and its Derivative Works and Digital Asset Data of Company’s Characters for acts or purposes offensive to public order and morals, for antisocial acts or purposes, for certain beliefs or religion, or for making a political statement;
(5) Not using the Company’s Characters and its Derivative Works for profit-oriented adult-only content, service, and for advertisement etc. of such;