Automatically save draft after time

Hi

Im sure i saw this but after extensive searching i still can’t find it. Some way of maybe a plugin that automatically saves your post as a draft and re-writes it every few seconds/minutes or somthing?? Does that exist? Also if you’ve used gmail – if you have written anything it’ll ask you if you are sure you want to discard your message. Does anyone know how to make somthing similar to that for WordPress?

Thanks alot

Usayd