I am surprised, Rascal that you dismissed sara as a �lonely chatter�. Perhaps, if instead of taking umbrage you had advised her what you hoped to achieve, her advice could have been tailored more accurately to your needs.
Anyone who feels the need to anonymously post details of a grievance they may have with their employer (and, more so, who needs to ask others, via this site, where they should do so) can hardly appear less lonely.
Sara�s answer may well have been unwelcome. That�s the trouble with sites such as this. You cannot pick and choose what answers you receive or from whom you receive them.
If you want a more valid (and valued) response you should raise whatever problems you have with your boss directly with him or her. If you cannot do this then try your boss�s boss or your company�s HR people. If none of this is possible (because, say you work in a small or autocratic organisation) you must either put up with the situation or get out.
The action you propose is childish and ineffective. It is unlikely that your boss will get to know about your posting, and anybody reading it will not have a clue who you are or who you are talking about.
I suppose you have in mind an equivalent of "Trip Advisor". Something like "Boss Advisor", perhaps. So the more succinct answer to your question is I do not believe (unsurprisingly) that there are any such sites.