MoonPlayer
MoonPlayer is a free and open source video player for playing and downloading online videos from YouTube, Youku, and iQiyi, as well as local videos
MPlayer
MPlayer – free and open source, cross-platform media player
QMPlay2
QMPlay2 – free and open source, multiplatform video and audio player which can play most formats and codecs
Celluloid
Celluloid – free and open source, simple media player that can play virtually all video and audio formats, GTK+ frontend for mpv
SMPlayer
SMPlayer – free and open source media player with built-in codecs, with support for Youtube for Windows and Linux
VLC
VLC – free and open source cross-platform powerful multimedia player which plays most multimedia formats