You can get the Alan interpreter from the if-archive/programming/alan/executables directory on the IF Archive. Download the MacGlk-Alan-nnn.sit.hqx file, where nnn is the version number of the program, and run the file through StuffIt Expander.
TADS 3 is the still-in-progress update to TADS. Luckily for you, if you downloaded the HyperTADS interpreter, you've already got an interpreter which will run TADS 3 games.
This isn't actually an interpreter, but rather a must-have utility written by Andrew Plotkin. Here's how it works: download IFDropFile. Then, if you ever get a game which shows up as a blank icon or as a SimpleText document, drop the game on IFDropFile. It'll set the Mac type information so that you can double-click the game in order to run it. How about that?