Wontube offers Free Video Converter that is a freeware helps you convert video formats. If you want to easy convert video formats, this is a good choice, even you don't have any skill you still can do it. Just download and install, pick a video file that you want to convert, choose a format, click "Convert" button, all done. It supports multiple video formats. If you want to convert Youtube video, just copy and paste video link, it will download video first, then you can convert it. Very convenient.
If you don't want to download and install anything in your computer, you can use web based Youtube Downloader - Share Youtube Video, it can download video from Youtube. Want to download music from Youtube? No problem, just go to Share Youtube MP3, easy to download.