Most Virtual Studio Technology (VST) effects can be used in real time or written (printed) to the audio file (I think that is what you were after). They can also take the form of virtual instruments (like synths).

For a full description check this link:

http://en.wikipedia.org/wiki/Virtual_Studio_Technology

Digidesign (the ProTools people) do two versions of their fiendish software. One (the little version) soaks up system resources. The full professional Pro Tools uses expansion cards and keeps all its workings away from the regular system resources.

You can get both for win or mac however for a fully kited out version of the full system you can easily part with 100 K !
It is also worth mentioning their is not much you can do on a fully equipped Protools system than you cant do with Sonar running Waves native gold and auto-tune. Much cheaper also (Sonar ~700. Gold ~1000, Autotune ~300) ! One thing to look out for the Sonar EULA is not transferable so if you get sick of it, you cant sell it. Crap eh !! Cake walk also love to charge you for little extras like MP3 encoders ! Bloody cheek after shelling out 700 bucks for the full version of their software !!

I was using the above however I have recently swapped over to Mac as I much prefer the hardware !! Unfortunately Sonar 4 Producers edition only runs on a PC. I thought about a PC emulating package but eventually came to the conclusion that I was following the path of ever decreasing circles and that if I wanted to do something well do it properly or go back to bed !