If public sector billing software is thought to be tiered in the same way as ERP software then the same two players are in Tier 1 - SAP and Oracle.  However property tax and utility billing software is a niche application; success with an ERP product does not mean that the billing product will be anywhere near the best available.  A quick Google or Live search for “water billing software”, for example, will produce multiple pages of possibilities.  Despite the consolidation mentioned previously, in the North American market there are abundant choices.  The same is true for property tax billing.  Municipalities and publicly-owned utilities should seek expert advice when [1] selecting a new billing system.