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.
The GNOME Structured File Library is a utility library for reading and writing structured file formats. Support for MS OLE2 streams is complete, as is zip import. There is also support for document metadata and some initial work on decompressing VBA streams in OLE files for future conversion to other languages. This library replaces libole2 and is used in gnumeric, mrproject, abiword, libwv2, koffice. It is also part of the AAF format.
rubrica is an address book written using GTK+ and GNOME. It allows you to add personal data (name, surname, address, etc.), Web links, email addresses, telephone numbers, job information (company where contact works, company infos, contact's assigment, etc.) and notes. XML is used to store the data. It can import addressbooks from GnomeCard and export to HTML.