Yeah first you had YouTube events, which I think were added last year, then we got YouTube Stream Now and more recently YouTube Gaming.
YouTube Events: Streams that start at a certain time as dictated by the time the stream set as the event start time, good if you want to provide notice of when you will be streaming.
YouTube Stream Now: As the name implies allows you to Stream whenever without going through the process of setting up an event.
YouTube Gaming: The same as Stream Now just that it has its own webpage that only shows gaming streams.