Since June 2012 (#342) youtube-dl is packed as an executable zipfile, simply unzip it (might need renaming to youtube-dl.zip first on some systems) or clone the git repository, as laid out above.
youtube-dl is a command-line program to download videos from YouTube.com and a few more sites. It requires the Python interpreter, version 2.6, 2.7, or 3.2+, and it is not platform specific. It should work on your Unix box, on Windows or on macOS.
yt-dlp is a feature-rich command-line audio/video downloader with support for thousands of sites. The project is a fork of youtube-dl based on the now inactive youtube-dlc. You can install yt-dlp using the binaries, pip or one using a third-party package