At the yesterday event, besides all the iPad and Mac news, Apple also announced that its SDK for the upcoming Apple Watch is getting released this November. However, when Tim Cook made the announcement, he didn't care to specify the exact date.
The Apple Watch SDK is called WatchKit and will be made available for developers next month. So, what this basically means is that iOS developers from all over the world will be able to develop their own apps for the upcoming Apple Watch.
They can choose to create new ones, but most likely what many will try to do is to accomodate already popular iPhone and iPad apps to the tiny screen of the Apple Watch.
Prior to the launch of WatchKit, Apple has only worked with select partners to build Apple Watch apps like BMW, American Express and Starwood Hotels. But now the doors are going to be open to all the developers.
The Apple Watch still has an official ship date of early 2015, since a new release date hasn't been offered at the event.