Billing solutions for ISP/VOIP/WIFI:
[http://www.rodopi.com Rodopi] Top billing solution for ISP, WISP, VOIP. Prepaid and Postpaid. Written in C++.
[http://www.aradial.com Rodopi & Aradial Radius server] A joint solution from Aradial and Rodopi for IP Billing. Written in C++.
[http://www.aradial.com Hosted Radius server and AAA Billing] A joint solution from Aradial and Rodopi for IP Billing. The Billing is Hosted by Rodopi. Written in C++.
[http://www.advancedispbilling.com Advanced isp billing] Billing for ISP, writen in Java/Tomcat.
[http://www.cwispy.net Cwisp] Free Billing for ISP.