Billd is a complete open source billing system for ICRadius written in C.
Includes billing daemon with support for variuos billing methods, support for pre-paid cards and administration tools
for users management.
MoneyTrack is a personal financial recording system, means it keeps track of your incomes / expenses via a database which can be accessed in different ways. There are several frontends available (web frontend, java-client, ...).
The purpose of this project is to develop an open source receipt program that will record receipt data and allow it to be viewed/filtered/sorted. There is also a PalmOS application to allow PDA data entry (and subsequent importing) while away from home.