DamnVid is a cross-platform application to download and convert videos from your hard drive or from dozens of video sharing websites.
DamnVid is a video converter, first and foremost. It makes use of the wonderful FFmpeg library, used in other software like VLC Media Player or Google Chrome. It is also a video downloader; while DamnVid can convert local video files just fine, it can also download video streams from most video sharing websites. But what gives it the edge over other video downloaders and converters is that not only it does both the downloading and the converting, but it does them at the same time: it converts as it downloads, making the whole process much faster.
DamnVid is also cross-platform, so you can also use it on Windows and Linux.