Grid is a startup app for the iPad and iPhone designed around how people use these devices and spreadsheets themselves. This is the complete opposite to a solution that makes Excel available on a tablet or smartphone.
At this stage the ability to actually perform calculations is a future feature. This isn't as odd as it sounds, since the beauty of the spreadsheet on a PC is that people use them in many different way - I know someone who even uses them for basic wireframing! They describe it this way:
Life is more than just numbers. In GRID: pictures, movies, people, locations and many more things are kinda of a big deal. Grid allows you to organize and work with them in a whole new intuitive way.
The second interesting aspect of Grid is the Maestro input system, which:
...takes away the need to dig into menus to find what you want, just swipe left to put things in and swipe right to do fancy things with them like changing how something looks and etc
It remains to be seen how popular Grid will actually be, but I can't fault them for approaching the problem the way they have. Personally the main limitation I see is that Grid may try to guess how people will actually use it - but the automatic connections to a finite set of existing data sources may end up being a constraint that reduces its utility. I hope they can make it as extensible as possible, to increase that utility - the more users can do the unexpected with it, the better.