From middle school girls’ sleepovers to more codified groups like the “Ladies’ Four O’Clock Club,” women have known for ages that there’s something special about the conversational dynamic that happens when a group of females get together. Above all, when women are in the company of other women that they trust, they often can be completely honest and comfortable in a way that they may not be in more mixed company.A website called Women.com aims to be the go-to place where women can speak honestly with each other online, deliberately away from the male gender — a sort of Ladies Four O’Clock Club for the online world. The bootstrapped startup, which is co-founded by CEO Susan Johnson and CTO Neal Kemp, is launching this week out of the current class of Y Combinator.