Gnumeric is a spreadsheet application developed under the GNU General Public License. This means Gnumeric is free and completely open source. It is based in GNOME, a desktop environment designed for open source software. As such, the interface widgets are very similar to those of other GNOME programs. It is one of the best alternatives for a free spreadsheet program.
If you have ever used a spreadsheet application before, you will not feel lost using Gnumeric. In fact, it is so powerful and it includes so many features and options, that it seems to be a very expensive program and not a free software application. You can open and use Excel, Lotus, and Open Office spreadsheet files with Gnumeric, and all the macros and formulas that were created by these programs will also work here.
The main problem with this program is more of annoyance than anything else. When using some menus, some of the elements seem to take some time to appear (you must hover your mouse over them sometimes), and some windows open behind the main application. However, this is not a big problem, considering that the program is free. Gnumeric is one of the best spreadsheet programs out there, free or not.