cdnjs is a free distributed JS library delivery service.
Cloudinary is an end-to-end image- and video-management solution for websites and mobile apps, covering everything from image and video uploads, storage, manipulations, optimisations to delivery.
OWL Carousel is an enabled jQuery plugin that lets you create responsive carousel sliders.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.