NeoBill is a Web-based customer management and billing solution designed for Web hosting providers, particularly hosting resellers. It can create invoices, manage domains, and provides other services. It has an API for CPanel and for Domain Registrare for automatic domain registration.
DHCP Lease Query in PHP is a PHP class that will allow you to send DHCPLEASEQUERY packets to inquire about known leases from a remote DHCP server. It is similar in nature to ISC's OMAPI but without the hangs it creates, nor does it cause dhcpd to behave in a single-threaded fashion while talking to it. After all, it emulates an actual DHCP "helper" (relay agent) and, as such, all queries travel over IP. It is based on RFCs related to DHCP and follows the RFCs as closely as possible.