GCC's C, C++ and Fortran frontends are commercial products of at least Red Hat and SuSE, for example see https://developers.redhat.com/products/developertoolset/over... and https://suse.com/c/suse-linux-essentials-where-are-the-compi...

GCC's Go frontend is still commercially supported as part of RHEL7 but was replaced by the more popular Go implementation in later versions.

GCC's Java frontend used to be commercially supported in the days before OpenJDK.