Billing

Billing methods (How billing works, how funding works, how resource usage is calculated for billing purposes, etc.)
Possibly also explaining how to use the CORE and OnApp APIs to handle most of these tasks programmatically. I'm not sure that this is something we have right now, but some businesses may need it. I'm aware of the OnApp WHMCS plugin, so at the very least we might want to create a simple article that explains how to set it up for our implementation.