Cruxy Mux Video Converter
Convert from (m)any video format to any other.
There's no dearth of freeware tools available for video conversion these days, with sporadic levels of success. Download.com is your friend with the search keyword "video converter".
But you need to download them, feed them the video you wish to convert (which means you need to have downloaded the video on your computer — I use the excellent VideoDownloader extension on Firefox when I must do this), and wait for the converted video to be created on your desktop. Altogether a cycle that requires the presence of several bits of software on your machine.
This is why I like the Cruxy Mux Video Converter. As you'll see in the immensely exciting screenshot below, you only need to specify the URL of your video (Youtube, Google Video, and such URLs are welcome), specify one of the formats available (all necessary ones are), and press Submit. Voila. It'll send you an email when it's done.
I promptly went and gave it a shot with the Burusu Wirrisu video on Youtube (Japanese Bruce Willis look-alike). I had the email in less than five minutes. Nice.
Nifty Feature: Second Life Mux!
To sweeten the deal, there's the Second Life Mux that will result in a URL "that can be used by land owners as their parcel's media stream for one day". Brilliant.