As for Linux, well, I don't think you'll go far there with proprietary programs. But let's assume a .NET like open source initiative. I'd give IE the application a pretty small market share then, but see no problem at all with programs using the rendering engine, i.e. a common "libIE" dependency.
(And, of course, if it actually is the same engine as on Windows, testing alone would guarantee a lot of installations)
[1] http://en.wikipedia.org/wiki/Tasman_%28layout_engine%29 [2] http://en.wikipedia.org/wiki/Internet_Explorer_for_UNIX
Huh, really. When was this then? I remember from during my veteran days of the browser wars (2005-2008 or so), IE for Mac was the only browser that PPK (of the Quirksmode.org compatibility tables) actually outright dismissed and at some point stopped testing for. If I remember correctly, his words were "bug-ridden crash-prone piece of trash".
While I wouldn't generally praise (any of) the browsers of that time, Macs really didn't have much competition at that time when it came to web browsers.
Hey Michelangelo, sign up for my art class and I'll show you how it's done.