short: Numerical data analysis framework - general applications
long:
From the web page (http://root.cern.ch/):

The ROOT system provides a set of OO frameworks with all the
functionality needed to handle and analyse large amounts of data in a
very efficient way. Having the data defined as a set of objects,
specialised storage methods are used to get direct access to the
separate attributes of the selected objects, without having to touch
the bulk of the data. Included are histograming methods in 1, 2 and 3
dimensions, curve fitting, function evaluation, minimisation, graphics
and visualisation classes to allow the easy setup of an analysis
system that can query and process the data interactively or in batch
mode.

Thanks to the built in CINT C++ interpreter the command language, the
scripting, or macro, language and the programming language are all
C++. The interpreter allows for fast prototyping of the macros since
it removes the time consuming compile/link cycle. It also provides a
good environment to learn C++. If more performance is needed the
interactively developed macros can be compiled using a C++ compiler.

The system has been designed in such a way that it can query its
databases in parallel on MPP machines or on clusters of workstations
or high-end PC's. ROOT is an open system that can be dynamically
extended by linking external libraries. This makes ROOT a premier
platform on which to build data acquisition, simulation and data
analysis systems.
