Well, I am sure there are programs and even good free ones to do it (like MyBB, WordPress etc..). Nonetheless, it would be tough to make a network to even slightly rival the big ones. However, though, who cares? It's all about fun, right? O.K., who has attempted to make a social network? How many joined it? How much activity did it have? How much profit did it make?
Who has thought about doing this stuff?
Who has thought about doing this stuff?