Gnumeric is a spreadsheet application with advanced features and
analytics. It aims to minimize the cost of transition from proprietary
spreadsheets by offering a familiar look and feature set. In addition
to read and write support for all versions of Microsoft Excel
(including reading encrypted files), there is also support for many
other formats including:

*Applix 4 and 5 *DIF *Lotus-123 (wk1, wk2, wk3) *OpenOffice.org (Oasis)
*PlanPerfect (pln) *Quattro Pro (wb1, wb2, wb3) *SYLK *XBase/DB3

Text formats, such as comma or tab separated values, HTML, XHTML, and
Latex, are supported and there are powerful assistants to handle custom
needs.

Gnumeric is part of the GNOME project.