The card readers need no software, they just attach and provide a means for the various cards to be read by your Mac. If you are reading memory cards they are read by the Mac as external drives, and should be ejected before removing them like all attached drives, or you may damage the card. These cards usually carry just standard data files; photo, music, video, etc. and are easily used by the Mac in iPhoto, iTunes, etc.
If you are reading a SIM card you most likely need software for the Mac to do that, just to access the data it carries, and so as not to damage it.
Dah•veed