Computational Quantum Chemistry is an active topic since almost 100 years and has driven development of both hardware and software (see e.g. Hartree). This community have pioneered the modern collaborative way of sharing codes and data.
Despite these facts and despite that many coding projects in active development have their own discussion group, there is no (in my knowledge) general public forum devoted to Computational Chemistry Code.
Both users and developper could benefit of that community where inter-projects would be possible.
While there is not a forum specifically dedicated to Computational Chemistry, both Chemistry SE and the newer Matter Modeling SE both accept a large number of computational chemistry questions, with Matter Modeling having a greater emphasis on the code side.
As mentioned, Computational Science SE can also address some of these questions, but it tends to focus on algorithm and implementation details without the surrounding physical context.