Thanks to the efforts of Iain Merrick and Andrew Pontious, there's a nice HTML TADS interpreter for the Mac called HyperTADS. Near the bottom of the HyperTADS page is a link to the latest version. It's in a StuffIt file. Download, unStuff, and put the resulting HyperTADS executable in a folder on your hard drive. Then throw away the StuffIt file you downloaded and you're ready to go.
There are two popular z-machine interpreters available for Macs, Zoom and Spatterlight. Both handle Glulx and z-code games.
You can get Zoom from Andrew Hunter's pages.
Spatterlight can be found at Tor Andersson's pages.
The latest version of the Hugo interpreter lives in the if-archive/programming/hugo/executables directory of the IF Archive. Look for the wxWindows version of the interpreter hugovnn_wxwin_mac.sit, where nn is the version number of the program. Download and unStuff as per usual.
Though AGT was originally only available under DOS, Robert Masenten wrote a more portable version of the interpreter and called it AGiliTy. You can download it from the if-archive/programming/agt/agility directory of the IF Archive. Download the MacAgility_n.nn.sit.bin file, where n.nn is the version number of the program. By now I trust you know the drill.