Y Combinator is renowned in Silicon Valley for a lot of reasons, but there’s one service that has quietly become one of its most powerful: an online founder-matching tool. “I think this is the most valuable digital product that YC has built (i.e. more valuable than Bookface, etc.). It’s astonishing how many founders I meet who met each other on the YC co-founder matching platform,” tweeted seed investor Nikhil Basu Trivedi. (Bookface refers to YC’s famed online collection of how-to startup advic...