Here are a few pieces of C++ code that I have written with re-usability in mind. Most of them do not carefully use namespaces to separate them as a library, but I have tried to create them with the idea that either myself or someone else could pick them up in a couple of years time and get them working in a few minutes.
Simple Debug Class - Here is a working, easy to use debug class that does not eat many CPU cycles unless debugging is enabled.
Simple Geometry Classes - some of these could be handled by compiling against ROOT, but not only is that complicated, it does not provide all the geometric transformations that are useful in astrophysical work.
C++ GSL Wrappers - although a couple of projects on the web have partially complete GSL wrappers, I found myself writing Object-Oriented C++ wrappers for the Bessel Function, Integration, Maximization and Interpolation functions from the GNU Scientific Library
alt2depth - a quick utility that converts altitude in meters to atmospheric depth in g/cm^2.
Simple Shower-Track Visualization - OK, I tried to link against ROOT to do some simple visualizations, but found an extremely steep learning curve. I wrote a couple of VERY simple classes for drawing particle tracks using OpenGL.
C++ GEOPACK Wrapper - a simple wrapper to enable calling the FORTRAN GEOPACK routines to calculate the Geomagnetic Field.
