Beets is a media library management system designed for obsessive-compulsive music geeks. It catalogs your collection, automatically improving its metadata as it goes using the MusicBrainz database. It also downloads cover art for albums it imports. Then it provides a bouquet of tools for manipulating and accessing your music. Beets also includes a music player that speaks the MPD protocol, so you can play music in your beets library using any MPD client.
Arista is an easy-to-use multimedia transcoder for the GNOME desktop. It focuses on the goal of transcoding media, namely the devices you wish to play the media on. It is designed for use by people who are not familiar with audio and video encoding and want an easy way to get multimedia to their devices. It supports input from DVD and V4L devices as well as regular files.
gst123 is a GStreamer-based command line audio player in the style of mpg123 and ogg123. The advantage over these tools is that gst123 can play every file GStreamer can, so mixed music collections with FLAC, Ogg, and MP3 files are no problem. Newer versions of gst123 additionally provide support for playing video files, while the ability to use gst123 without X11 display has been preserved.
audiopreview is a command-line tool that plays previews of many audio file types (Ogg, MP3, etc.), video file types (AVI, MPEG, Real, etc.), and Internet streams. It can also be used as a regular command-line media file player (i.e. play the files entirely like yauap or mpc123 would).
Voody Blue Subtitler is a suit of programs that allows you to manually synchronize a text file with a video stream, thus creating a subtitles file. It consists of a master client (to do the sync), a slave client (projector), a relay server, and a configuration utility. It runs on Linux and Windows (all except the relay server), supports video output via GStreamer (Linux and Windows) and MPlayer (on Linux only), and supports GTK+ 2 and 3 (decided at compile time).
Epris is a D-Bus service and command line client to listen to music. Unlike xmms2 or mpd, it uses GStreamer and D-Bus. It supports all formats supported by GStreamer, and can play both video and audio. It supports gap-less playback thanks to playbin2. It has an extensible command line interface, a small memory footprint, automatic deactivation, and an easy D-Bus interface for other UIs.