(This notice has been updated repeatedly to discuss: OS X 10.2, Adobe app bugs with 10.2 support, "cocoa" applications; Adobe phasing out MM font sales; Adobe discontinuing tech support for MM fonts. Last update: 23 Sep 2005.)
With versions 10.0 and 10.1, Mac OS X's native support for Type 1 and OpenType initially failed to include support for multiple master Type 1 fonts. This problem is fixed in OS X version 10.2 and later for applications using the "carbon" APIs, but not for applications using "cocoa" APIs. The two most common "cocoa" applications are TextEdit and Keynote.
Note that applications running in "Classic" mode are unaffected. They still need ATM for supporting Type 1 fonts, including multiple master fonts.
There is a workaround for some Adobe applications, such as InDesign 2, Illustrator 10 and Photoshop 7. You can rely on the native font imaging support in these applications, which is largely independent of the OS. Just put the fonts in the the Fonts folder in the application's folder, or the Application Support/Adobe/Fonts folder.
Additionally, the above-mentioned Adobe applications may have problems accessing all multiple master instances, when accessing the MM fonts which are installed at the system level, even in Mac OS X 10.2 and later. In some cases, this may be worked around by installing the fonts in the application's own fonts folder or the Application Support folder as described above.
PHASING OUT MULTIPLE MASTER FONTS
Adobe stopped making new MM and Type 1 fonts in 1999, and there is no equivalent to MM in the newer OpenType format. From late 2002 to mid 2003, Adobe phased out sales of multiple master fonts. As of this writing, they can only be bought from Adobe as part of Font Folio 9, which is still available for people who need compatibility with older fonts. The current version of Font Folio is Font Folio OpenType Edition, which shipped in August 2003.
At the end of 2004, Adobe stopped offering tech support for MM fonts, excepting for people with Font folio 9.