I'm curious about the software, because in my experience these kinds of things are doomed projects.
Yahoo had at least four internal websites devoted to companywide skill-sharing. Google had a couple of these too. I don't recall them ever being useful.
They are started by naive new engineers who get frustrated because they can't get anything done. They think everyone's going to be thrilled to create a profile, say publicly what they are good at, and to answer questions from effective strangers. But it never works.
A year later they have personal relationships within the company, and know how to use those instead. And this is what motivates people to really help.
So do you think software is going to work better within the YC community? Maybe there's some communal spirit there that can overcome that tendency, due to all the dinners together or everyone knowing the YC partners. Or maybe your network is just small enough, and has higher-than-average quality people, so people would care about their reputation for helping strangers.