The one with the blue background might be
Composer Headquarters :: Index (I think they had a different skin a while ago?)
Anyway, Composers Headquarter's has 35 members in total, not even remotely compared to the 4 digit amount of YC users (some 4,169 registered users, atm).
However I must say that I am afraid the actual amount of active users in YC wouldn't be more than, say, 50.
The reason I haven't been active in CH is because of the shameless promotion they did the other week. Instead of promoting something good that they do, they tried to show how bad YC was, which is something I despise in general.
Anyway... here I am..