Minuit2, originally developed in the SEAL project, is now distributed within ROOT. The API has been then changed in this new version to follow the ROOT coding convention (function names starting with capital letters) and the classes have been moved inside the namespace ROOT::Minuit2. In addition, the ROOT distribution contains classes needed to integrate Minuit2 in the ROOT framework.
In the latest version (from 5.17.08) a new class has been introduced, ROOT::Minuit2::Minuit2Minimizer, which implements the interface ROOT::Math::Minimizer. Within ROOT, it can be instantiates also using the ROOT plug-in manager. This class provides a convenient entry point for using Minuit2. An example of using this interface is the test program
The current version of Minuit2 (indipendent of ROOT) can be downloaded from here and does not contain the ROOT interface. It is therefore totally independent of external packages and can be simply build using the configure script and then make. Example tests are provided in the directory test/MnSim and test/MnTutorial and they can be built with the make check command.
The User Guide provides all the information needed for using directly (without add-on packages like ROOT) the C++ version of MINUIT.