Dunno about Excel or Word, but I remember something about using Abiword or something like that to convert .doc files into a format the n800 could read. As for a calendar, try GPE Calendar, it can sync with Google if you use ermming.

For stocks you could try finding an applet (I don't check my stocks often so i don't bother with them) as for games there is a game section in this forum. You can also try going to maemo.org and going to the games section to install their games. I personally like sudoku (yeah, sounds fun I know :P) and bomberman. There's a GBA emulator but it's rather slow. Battle of Wesmoth? is a fun turn based strategy RPG game. I can't remember the exact name is also fun, I have it on my Ubuntu Linux installs but not on my tablet since it's running OS2008 and not OS2007 (which the version that you can find on here requires).