If you are searching for a way to download youtube videos on your Macbook Pro/Macbook Air/iMac without software or apps installation, then use your web browser to complete the task. Just make sure you have installed Java Runtime Environment and Restarted the web browser once to make it work as the website use Java to run this youtube download tool. This is completely web based, and you dont have to install any youtube video downloader or youtube video download software/apps on your mac computer.
There are many websites but i find keepvid as my favorite on any OS platform. Even in Windows and Linux i prefer this website as it offers high quality video download solution that is very compatible for iPhone, iPad and any Android smartphone, tablets. This is one of the best youtube video software alternative to download videos online without installing any apps on your Macbook Pro, Macbook Air and iMac.