HostBill 3.8.0 has just been released, make sure to check whats new:
OnApp & OnApp CDN: Pre-Paid Metered billing
Let your customers pay upfront for resources, invoices can be generated after account credit will reach your threshold.
New module: Observium
Now you can add bandwidth billing trough Observium, an alternative to previously released Cacti integration. Allow clients to browse graphs, estimate & bill for overages. Learn more at http://hostbillapp.com/features/colocation.php
New, Easy Development Kit
Building module for HostBill has never been easier – no object oriented programming skills required – simple function calls, well documented at http://dev.hostbillapp.com/procedural-dev-kit/ allows you to create fully functional module with few lines of code.
Full changelog: http://hostbillapp.com/changelog/