This article is from the Mac Programming FAQ, by Jon Watte firstname.lastname@example.org with numerous contributions by others.
Apart from the libraries mentioned above, there are three contenders:
MacApp, TCL, and PowerPlant. "Bedrock" will never be released as a
product, although parts of it surface in TCL 2.0 and other parts will be
the base for the OpenDoc Parts Framework.
MacApp is a heavy-duty class library that has tons of features and a
steep learning curve; it runs under MPW with Pascal or C++, and also
under Think Pascal 4.0 A major application written in MacApp is
TCL stands for Think Class Library and comes with Think Pascal, C or
C++. It is a smaller library that still fills most peoples needs; since
Think C implements a subset of C++ (the most important OO concepts such
as virtual functions and inheritance) and the TCL is carefully written
not to take advantage of any C++ features not in Think C, you can use it
with Think C. A major application written in TCL is Lotus 1-2-3. (TCL