Why is GnuCash written in C?
The core functionality of GnuCash is written in C, but do not forget that much of this can be accessed through Guile (scheme). There are a number of reasons for why GnuCash is written in C. The first is historical, Gnucash was started in 1996 (or maybe even earlier!) and many of the OOP (C++, Java, Python) compilers were not yet mature and standarized enough on the variety of platforms considered at that time, so C was the only option at that time. A second reason is because the standard GUI GnuCash uses is GTK, which is written in C.