Welcome to the official documentation for Gears. You can find all the documentation for classes and functions in the annotated view.
Gears is a collection of utilities (henceforth now called "modules") that are helpful to C++11 programmers. These include a large collection of modules ranging from the string module to the functional module.
Since Gears makes heavy use of C++11 features, only the compilers with the most support for C++11 are supported. At the time of this writing, this only includes GCC 4.8.1 or higher and Clang 3.4 or higher. Visual Studio 2012 or lower are not supported at all, and you might get lucky with some modules on Visual Studio 2013 although not explicitly supported.