Because The Linux Sound User's Guide describes the available Linux applications in detail, I will only give here a sample of the types of applications that you likely want if you have a sound card under Linux.
As a minimum, you will likely want to obtain the following sound applications:
Sox
)aumix
or xmix
)play
)tracker
)mp
)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) that you may wish to try.