An API that allows applications to support Open Financial eXchange command responses, usually provided by financial institutions for bank statement downloads.
The GnuCash Project aims to develop GPL'ed financial/accounting software modules. GnuCash itself is a Gnome Desktop application aimed at personal finances and home users.
GeniusTrader is a perlbased, GPL-software for the creation of trading systems and to backtest them. It also includes a large database of common indicators and signals and is capable of displaying all the stuff in various formats.