Historically these have been, for the most part, Windows based programs. While in the past this usually was not an issue, the number of Apple/Mac clients I have seen of late is quite significant. Fortunately, the AT companies have been ahead of the curve and the vast majority of these tools are available for Mac as well.
Here is what is currently available on Mac:
Kurzweil
MacSpeech Dictate is Nuance's MAC version of Dragon Naturally Speaking
And don't forget that Mac has alternatives to Word, Excel, and Powerpoint in their iWork package.