Download Link / Website: http://www.xenra.com
Yes that are many tools that can be utilized to perform this task. For example one can download the youtube video and then extract the audio out using some tool, but why the hassle?
This website does all the work for you and lets you download the MP3 straight. Conversion to other video formats is also supported.
1) At the website, paste your youtube link and click 'Download Now'
2) In the next screen select your desired output video format to convert to (default selected as MP3) and click 'Start Conversion'.
3) Go get a cup of coffee while they prepare your file :) Click the big download button when it's ready.