VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Netflix Party - Netflix Party is an extension for watching Netflix remotely with friends and family for movies nights with that long-distance special someone.
foobar2000 - An advanced freeware audio player for the Windows platform.
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.
Winamp - Winamp is a media player that allows users to play multiple-file formats, arrange media in a varied file-management system, and play unique media with AAC encoding.
Metastream - Watch streaming media with friends