Movgrab is a command-line movie downloader for sites like YouTube. It has no dependencies; everything that's needed should be there in the tar.gz package. Movgrab can connect through an HTTP proxy, can output the download to stdout for piping into another program, and can fork into the background to free up the console. When forked into the background, its progress can still be seen in a ps list.
Videomanager is a Web-based video manager. It's not a Youtube/Vimeo clone, it just provides the core functionality of uploading, converting, and displaying videos. Commercial support is also available, as well as enterprise features like distributed rendering, tracking, and live streaming.
Minitube is a YouTube application for Mac, Linux, and Windows. With it, you can watch YouTube videos in a new way: you type a keyword, and Minitube gives you an endless video stream. Minitube does not require the Flash Player. It is not about cloning the original YouTube Web interface, but strives to create a new TV-like experience.