Behind the obabel command line program lies a complete cheminformatics toolkit, the Open Babel library. Using this library, you can write your own custom scripts and software for yourself or others.
Any software that uses the Open Babel library must abide by terms of the GNU Public License version 2. This includes all of the supporting language bindings (for example, Python scripts) as well as C++ programs. To summarise, if you are considering distributing your software to other people, you must make your source code available to them on request.
Open Babel is a C++ library and can easily be used from C++. In addition it can be accessed from Python, Perl, Ruby, CSharp and Java. These are referred to as language bindings (the Python bindings, etc.) and they were automatically generated from the C++ library using SWIG. For Python we also provide a module (Pybel) that makes it easier to access features of the bindings.