chenyufei -
Gnumeric is a spreadsheet ported to OS2008; under OS2007 it had Excel support, but that seems to be a bit buggy the last time I heard. I don't use it to create files that I then use with Excel.
Abiword is a word processor that could read Word files; someone is working on porting it to OS2008
No presentation software that I know of.
I also use Maemopad+ as a sort of note taking application that can do lists and line drawings.