GnuCash is a personal and small-business finance manager with a check-book like register GUI to enter and track bank accounts, stocks, income and expenses. GnuCash is designed to be simple and easy to use but still based on formal accounting principles.
Account Guard helps you monitoring your expenses. Spend a few minutes every other day with an easy to use GUI and it will tell you where you can improve on your financial situation. Core is a simple but complete library for single-user data-applications.