AmigaOS:
*GCC - Just got into programming
*PPaint - Still a good for web graphics ad anims
*Cinema4D - Old creaky raytracer but still easy to use.
*Webplug - Superb HTML editor with many great function (stuck at beta unfortunately :-( )
*EditPad - Does it's Job
*Shell - Does it's job, AmigaOS still has the best CLI ever, I used to use VNC but got fed up with it.
Windows:
*WinUAE - Enough said, actully that's all I use it for.
MacOS X:
*Mail - Nearly up there with YAM
*Safari - Very nice Web bowser much leaner than IE or Moz yet with all the features
*iTunes - Great MP3 Player, made me a convert to digital music.
*iChat - AIM client that fits in with the system nicely
*XChat - Port of the IRC client
*Photoshop - Enough said, how did I ever get by without it?
*BBEdit Lite - OKish Text editor
*OpenOffice - Pretty good, but needs X11 to run and so is a bit clunky, I'm looking forward to the native Aqua version due next year.
*iPhoto - just plug in my camera and iPhoto takes care of the rest :-) I don't have to use a driver or anything.
Fequency wise, I use most of the stuff listed every day. My Mac is the main machine for most things so I use those programs the most (execpt iPhoto which is only when I've taken pictures) The Amiga proves itself useful most days too :-)