You-Get - Command-line utility to download media contents from the web
Waybackpack - Download the entire Wayback Machine archive for a given URL
CONV. - Convert YouTube video to MP3, GIF or MP4
YouTube Decade - Watch the most viewed videos posted exactly 10 years ago
Softorino YouTube Converter - Download YouTube video & audio. Watch and listen offline
ArchiveBox - The open-source, self-hosted internet archiving solution