A nice software based MIDI player. Notable for eating large quantities of CPU time, producing nice music and having about a million different interfaces.
The packaged version with most distributions seem to be rather out of date, so it's best to compile from source. This additionally allows you to choose which interfaces to compile. There is a Debian package of free sound samples which saves hunting 'round the net for them.
Interface choices include: command line, curses, GTK, Tcl/Tk and emacs!
Available from http://www.goice.co.jp/member/mo/timidity/.