My, how Y Combinator has grown. It wasn’t that long ago that the prestigious startup incubator had a dozen or so startups per batch. These days, class sizes are more like 60, and the alumni network is huge: in total, Y Combinator has invested in some 317 startups. Given how many YC startups there are, it isn’t really surprising that a lot of them have some overlap, or are at least tackling similar problems. Today, YC is announcing an event that’s taking advantage of that fact: the Ad Innovation Conference. The event, which takes place on September 14, will feature fifteen YC companies involved in building new ad-related technologies. Among the topics that will be covered: