If the question is can you download a third party app to the Apple Watch without a companion iPhone - no, you cannot. If the question is are there any third party apps that run only on the Apple Watch that do not have a companion iPhone app - no, there are not.
Thank you very much for your answers, sorry for the confusion. The question was 'can you download a third party app to the Apple Watch without a companion iPhone'
Thank you very much for your answers, sorry for the confusion. The question was 'can you download a third party app to the Apple Watch without a companion iPhone'
Right, apps are always installed via the Watch app on the iPhone. At least for now. Since they've added cellular capability, I wonder if a future release will be more stand-alone for app installs as well. Only time will tell.