Gnumeric is a powerful and easy to use spreadsheet using GNOME. Its goal is to provide a full featured spreadsheet and a smooth migration path for people and organizations currently using proprietary applications. It provides more sheet functions and greatly improved accuracy when compared to Microsoft's Excel. A plugin system lets you extend Gnumeric, adding functions, I/O formats, and real time data capabilities. The existing Python, Guile, and Perl plugins let you define complex functions. Gnumeric is capable of reading and writing MS Excel (XLS and Office Open XML), and reading Lotus, Applix, Quattro Pro, OpenCalc (ODF), XBase, DIF, SYLK, HTML, Psion, MPS, oleo, sc, misc. text formats, and its native XML. It can also generate Latex, HTML, and others.
XESS is a spreadsheet for UNIX, Linux, OpenVMS, and Windows NT which supports user-configurable 3-D workbooks with up to 10 million rows, enhanced display and print formatting, international locales (including multi-byte languages), full Y2K compliance, Web enablement, and a high level of compatibility with the Excel and Lotus spreadsheet products. It includes filters for Excel 97, Excel 2000, and Lotus spreadsheets.
xlHtml converts an Excel spreadsheet file (.xls) into highly-optimized HTML. It includes scripts to allow it to be used as a Netscape or mutt plugin and as a xls handler for Apache. The program currently supports string, blank, boolean, error, integer, floating point, hyperlinks, and formula cells. It can also output in XML, tab delimited, or comma separated values (CSV).
Sharp Tools is a spreadsheet written in Java. It features full formula support (nested functions, auto-updating, and relative/absolute addressing), a file format compatible with other spreadsheets, printing support, undo/redo, a clipboard, sorting, data exchange with Excel, histogram generation, and a built-in help system.
Spreadsheet::WriteExcel is a Perl module which can be used to create native Excel binary files. Formatted text and numbers can be written to multiple worksheets in a workbook. Formulas and functions are also supported. It is 100% Perl and doesn't require any Windows libraries or a copy of Excel. It will also work on the majority of Unix and Macintosh platforms. Generated files are compatible with Excel 97, 2000, 2002, and 2003, and with OpenOffice and Gnumeric. An older version also supports Excel 5/95.
QuantLib is a cross-platform, quantitative finance C++ library for modeling, pricing, trading, and risk management in real-life. It is also wrapped as Python/Ruby/Scheme modules. Extensions for Excel, R, and Mathematica are available. Other such extensions are under consideration. QuantLib offers tools that are useful both for practical implementation and for advanced modeling. It features market conventions, yield curve models, solvers, PDEs, Monte Carlo (low-discrepancy included), exotic options, VAR, and so on.