The name stands for "General Purpose Abstraction Layer". GPAL is a set of C++ classes which are used to represent any kind of data and to manipulate them. Thanks to SWIG, it is usable in many programming languages.
A script(ing/ed/able) optimizing compiler for the C and Objective-C languages (and in the future other languages such as C++, D and Java). Written in a scripting language to allow for experimentation with code generation and optimization techniques.