I give here a sample of the types of applications that you likely want if you have a sound card under Linux. You can check the Linux Software Map, Internet archive sites, and/or files on your Linux CD-ROM for more up to date information.
As a minimum, you will likely want to obtain the following sound applications:
audio file format conversion utility (e.g. sox)
mixer utility (e.g. aumix or xmix)
digitized file player/recorder (e.g. play or wavplay)
MOD file player (e.g. tracker)
MIDI file player (e.g. playmidi)
There are text-based as well as GUI-based versions of most of these tools. There are also some more esoteric applications (e.g. speech synthesis and recognition) that you may wish to try.