I use FreeOffice frequently because IMHO it's a fantastic office suite, and want to add some notes.
Christophe: Yes, there's also a free version of SoftMaker Office 2008, but it's outdated. FreeOffice is the current free office suite from SoftMaker, compared to SMO 2008 it has many improvements, e.g. better import and export filters for Microsoft Office files, which brings me to
Aleksej: There's no difference between FreeOffice for Windows, and the Linux version. Both versions of FreeOffice are able to open(!) docx, xlsx, and pptx files - faithfully!!, in contrast to LibreOffice, OpenOffice and others that either screw formatting, or don't open files at all.
It's just not possible to save (!) in current Microsoft Office formats. If you want to save as docx, xlsx, and pptx, you will have to purchase the "big" SoftMaker Office for Linux, which btw. has 1000 functionalities more, and is worth every penny. I just saw at the SoftMaker Facebook profile that the prices for upgrades were lowered, you pay $34,95 for three licenses, including free support!
FreeOffice is the best free office suite and good enough for most users, but if you are ambitious and need professional equipment, get SoftMaker Office for Linux, that's the ultimate.