We discuss the present state of XSPEC and CFITSIO, two of the more widely used packages in HEASOFT, the software suite maintained and distributed by the HEASARC at NASA/Goddard Space Flight Center. XSPEC is an interactive X-ray spectral fitting program that has been used in almost 10,000 refereed publications over the last three and a half decades, and underwent a full redesign in the 2000s to object-oriented C++. We examine its modular design which allows for the expansion of such capabilities as new fitting statistics, plotting packages, and models (including those supplied by the end-user). We also show how originally unanticipated features were incorporated into the design, such as parallel processing and an extension module providing full access to XSPEC from Python (PyXspec). CFITSIO is a C and Fortran library that is used in much astronomical software for performing fast operations on FITS files. It has recently undergone a transition in support from its original author to the HEASARC programming staff, and we discuss challenges this entails and also some of its recent enhancements.
Link to PDF (may not be available yet): P5-7.pdf