It's maybe a competitor for ThinkFree Office's spreadsheet, but Excel
is safe for now. No array formula support. Google Spreadsheet's (GS's)
online function list shows MMULT, but there's no way to use it, and
when it opens .xls files that do use it, it converts those cells to
values WITHOUT any warning that it has done so.

It also starts off with a capacious 20 columns by 100 rows. The number
of columns can be expanded to 256, but it takes several Insert commands
to do so. For that reason, I didn't bother checking how many rows it
could hold.

And commands/menus are all over the top of the screen.

Anyone interested should definitely compare it to ThinkFree,

http://www.thinkfree.com/common/main.tfo

as well as to Excel.