There no FREE alternatives! In fact there are no alternatives at all! MovieSherlock is much more than just "youtube downloader", however it can do that too.
MovieSherlock is fast and extremely easy to use application designed natively for Mac OS platform and YouTube and any other web sites that play video. MovieSherlock will search, download and convert any YouTube, DailyMotion, Vimeo, etc movies to your Mac native format. Downloaded videos will have correct file names. Other premium features includes multiple simultaneous downloads, built-in YouTube, Vimeo, DayliMotion search and preview capabilities, single-button user interface and unique convert features. Converted movies are added to your iTunes library automatically. After downloading you can easily copy videos to iPod, iPhone or iPad as they will be converted to Mac native format. Automatically adds downloaded video and audio to iTunes. You can even save the videos as MP3. Download 1080p and 720p HD videos as well as regular Youtube / Vimeo / DailyMotion / Facebook / MySpace / Yahoo!Screen / etc videos. MovieSherlock offers native interface in English, Italian, Spanish, French, Japanese. We provide 100% satisfaction warranty: if you will find a YouTube video that is not downloaded by MovieSherlock we will fix it or do full refund. The fact is, MovieSherlock Pro can download videos from Vimeo, DailyMotion and other web sites as well as it does from YouTube.
What's new in this version:
-Introduced Show Similar: loads up vides very similar to the selected one
-Introduced Safari Integration button
-Fixed download of Vimeo videos
-More concurrent download allowed
-Capture video from web browser
-Video Capture feature was moved to the release state.
-Dock notifications for downloading videos.
-Fixed issue with poor MP3 audio quality.