Pretending to be the non-free billing app
FusionPBX doesn't do billing or LCR out of the box, but one guy will sell you closed, proprietary, non-free billing and LCR modules that will integrate nicely into FusionPBX. To help with this, there are a number of places in the free FusionPBX codebase that run things that these non-free apps need. Obviously these are all completely undocumented, until now.
These work by checking for an app named "billing". Specifically, they look for the
file in the billing folder. The conditional usually looks like this: