In Open, you select your choice of default file formats to save in, and it will open pretty much everything. So I have all my defaults set to the MS equivalents (.doc/.docx/.xls etc) and I exchange files with clients all the time, no one has ever had any problems.
In Open, you get: Word processor (Word look a like), spreadsheet (Excel look a like), database (Access look a like), presentation (Powerpoint look a like) and a drawing program I've yet to use.
They are separate windows in their own right, and each one looks more like the MS version than the MS version. But when, for example, in the word bit, you ask for a new file it gives you the option of all the apps, not just the word flavours.
I now don't use a single bit of MS software apart from windows itself, not because I've anything against them but because there are genuinely better and free alternatives. Browser = Firefox, Email = Thunderbird, Office = Open Office. Oh, and as for Windows, if OS/2 were still alive today......... [waits for someone to say the word 'linux'....]