Great Downloader easy to use can convert into multiple file formats. Fast and impressive
VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Video DownloadHelper - Browser extension to download videos from the Web
MPV - MPV is an audio and movie player based on MPlayer and mplayer2.
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.
SMPlayer - SMPlayer is a free video and audio player for both Windows and Linux that allows you to play almost all media files without having to install additional codecs. Read more about SMPlayer.
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.