Airy is a useful app, which allows you to download and keep all your best YouTube videos at hand. It is a very good tool for downloading YouTube videos on the Windows platform. You can save your videos in different resolutions and file types. You can easily download full HD and 4K Ultra HD resolution videos to your hard drive and enjoy a them at any time you need them.

Key features include:

• You can keep the video and watch it even if the original uploader removed it from YouTube.
• You can watch HD videos without depending on connection speeds.
• You can transfer the video to watch it on mobile devices.
• You can extract MP3 audio out of video without keeping the video.
• Enjoy the freedom of sharing the video anytime anywhere.

Airy downloads MP4, WebM, FLV, and 3GP file types and it also can extract MP3 audio from YouTube videos; simply paste the YouTube link in Airy, choose MP3 from file types list and click 'Download'.

Airy's browser integration allows you to simply click a bookmark to add the video's URL to Airy for downloading.

Overall, the application is quite basic, which makes it easy to use, but it lacks many of the features and options that are common to YouTube downloaders, like drag-and-drop and batch processing. The trial version has some limitations and will only allow you to download 2 free YouTube videos to test out the app.