We don't offer a native version of Mp3tag for Mac OS X or Linux, but there are various possibilities to run Mp3tag under Mac OS X and Linux.
Mp3tag on Mac OS X
Under Mac OS X you can use the excellent WineBottler which allows for creating an Mp3tag.app that runs under X using Wine. Just create a new prefix, point to Mp3tag's installation file and go through the wizard. It's really quite straightforward. WineBottler is also Freeware, though donations are welcome.
Another option is to use CrossOver Mac which is basically a version of Wine maintained and professionally supported by CodeWeavers. It also officially supports other famous software products and if you need to run some of those programs on your Mac spending a few bucks for a license is probably an option for you.
Of course, there is always the possibility to run Mp3tag in a virtual machine running Windows. VMWare Fusion and Parallels are known to provide the best products there.
Mp3tag on Linux
On Linux you can simply install Wine (or compile the latest version yourself). If something stops working for you, just drop a note here in the forums. If you need to use Windows Media Audio (WMA) files, you need to install the Windows Media Runtime wmfdist.exe from Microsoft in Wine.