App for creating icons on computer?

I'm new to using these forums, etc. In fact, I really sort of "wing
it" in my use of Icon Mgr., in general. As I'm an artist, I find that
I do a pretty good job of 3D Hi-Res icons, but it does get exhausting.

In looking at a post from Dennis re:Tango Desktop Project, I followed
the link provided and saw that he apparently had some application on
his PC (or so it appeared by the window displayed in the snapshot of
his desktop). Additionally, I am on a Mac, not PC, so that may make a
difference if there is such an app available.

I'd always wondered if there weren't an application (or version of
Icon Mgr.) which could be utilized on the computer. My eyes get really
exhausted after awhile as I design icons on my Treo.

I'd sure appreciate any info you have. Many thanks.