It's open office also just not the latest version of openoffice plus it does not have any of the X11 dependencies. So you'll get all your aqua menus etc that you are used to. Eventually they will update it to use open office 2.x code, but until then it uses the previous release of open office as it's base code.
Open Office is the best and most compatible with everything out there.. has a lot of functionality, but has X11 dependencies and is not aquafied. Free. Slow to bootup, but nice once it's open.
Neo office based on older open office code, but is still really nice, and does not have the X11 dependencies, will work with all MS Office files again, save and edit. Free. Not as slow as Oo when booting, but still slow
iWork I've never used so I can't really tell you much of it. But I know it costs.
MS Office, expensive. Opens quickly and is compatible with itself and other file formats, bulky. Is not compatiable with saving in the open office format.