1. Gnumeric
The Gnumeric spreadsheet is part of the GNOME desktop environment: a project to create a free, user friendly desktop environment. The goal of Gnumeric is to be the best possible spreadsheet. We are not attempting to clone existing applications. However, Gnumeric can read files saved with other spreadsheets and we offer a customizable feel that attempts to minimize the costs of transition.
2. Oleo
Oleo has for a long time been GNU's spreadsheet. Now there's not only Oleo but also Gnumeric, the GNOME spreadsheet. Gnumeric is a full featured spreadsheet, aiming to compete with commercial applications, and well integrated with GNOME. Oleo is a light-weight spreadsheet that'll work in almost any environment.
3. KSpread
KSpread is a fully-featured calculation and spreadsheet tool. Use it to quickly create and calculate various business-related spreadsheets, such as income and expenditure, employee working hours…
4. Calc
CALC is the spreadsheet program you've always wanted. Newcomers find it intuitive and easy to learn; professional data miners and number crunchers will appreciate the comprehensive range of advanced functions.
5. Siag
Siag Office is a tightly integrated, free office package. It consists of the spreadsheet Siag, the word processor PW, the animation program Egon, the text editor XedPlus, the file manager Xfiler and the previewer Gvu.