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.
A quantitative finance C++ library for modeling, pricing, trading, and risk management in real-life. A cross-platform free/open-source tool for derivatives and financial engineering.
track time spent, keep a diary, to-do list, generate reports, bills
GnoTime (formerly GTT, the Gnome Time Tracker) is a desktop utility for tracking the amount of time spent on projects, keeping a to-do list, maintaining a diary, and generating reports and invoices based on that time.