MINUIT, now MINUIT2, is a numerical minimization computer program originally written in the FORTRAN programming language by CERN staff physicist Fred James in the 1970s. The program searches for minima in a user-defined function with respect to one or more parameters using several different methods as specified by the user. The original FORTRAN code was later ported to C++ by the ROOT project; both the FORTRAN and C++ versions are in use today. The program is very widely used in particle physics, and hundreds of published papers cite use of MINUIT. In the early 2000s Fred James started a project to implement MINUIT in C++ using object-oriented programming. The new MINUIT is an optional package (minuit2) in the ROOT release. As of October 2014 the latest version is 5.34.14, released on 24 January 2014. There is also a Java port as well as several Python ports.
MINUIT is not a program that can be distributed as an executable binary to be run by a relatively unskilled user: the user must write and compile a subroutine defining the function to be optimized, and oversee the optimization process.