GNU Radius is a RADIUS server and an accompanying set of monitoring utilities. It features MySQL and PostgreSQL interfaces for authentication and/or logging (the ODBC interface allows you to use almost any existing DBMS for that purpose), the ability to rewrite RADIUS requests from various NASs to normalize them to a more understandable format, and the ability to completely customize the behavior of RADIUS authentication and accounting based on NAS and user attributes.
GnuCash allows you to track bank accounts, stocks, income, and expenses. As quick and intuitive to use as a checkbook register, it is based on professional accounting principles to ensure balanced books and accurate reports. It is backed by an active development community and is blossoming into a full-fledged accounting system.
GnuLedger is a Web-based accounting system. It has all of the functionality that an average home user needs to manage their finances. Its backend is a MySQL database, and it currently uses a web browser front-end. It has been tested using Internet Explorer, Mozilla, Opera, and QNX's Voyager.
Grisbi is personal accounting software that can manage multiple accounts, multiple currencies, and multiple users. It manages third parties, expenditures and receipts categories, and also budgetary lines, financial years, and other information. It is adapted for personal use as well as for associations.
ISPacct (formerly Brickacct) accounts the logfiles which Bintec routers spew out depending upon configurable rules. Logfile-analyzing mail accounting functionality is also included (in beta stage). It has multiple backends like text, HTML, and MySQL. It was designed and used by a small ISP and is geared towards such uses as monthly accounting per IP or per dial-in use.