VIM is ported to the Mac by some enthusiasts.

VIM is an excellent VI clone, and IMO the best cross-platform programmers editor available.

While it is not KiXtart specific it does have KiXtart syntax files for colour highlighting.

The biggest advantage is that once you've learned how to use it you can use the same editor on Mac, Windows, Windows CE, OS/2, *nix, Amiga OS, and a few odd ones that I've never heard of.

Source code is provided, so you can compile it yourself if you have the environment.

Mac VIM details here: http://www.vim.org/download.php#mac