Excel is still the gold standard for ad-hoc analysis up to anything that needs a database. It’s also hugely popular for holding lists of anything.
Spreadsheets is, no surprise, an online spreadsheet. It can read and save to .xls and .xlsx files, but complex analyses and anything with VBA won’t work out well. Those more complex functions just don’t exist in Spreadsheets yet. Simpler files, up to and including Pivot Tables, work great. The big advantage of Spreadsheets is that multiple people can edit one file at the same time, which is super useful for compiling data in a team, or ensuring there’s only one copy of the file (no more merging changes). There are a few neat touching for pulling live data in, like live currency conversion data, that Excel isn’t so great at.
Office web apps
If you’re used to the look and feel of Excel, and you don’t need the more hardcore analysis tools, Microsoft provide a version of Excel for the web. It’s in beta, but it works pretty well. Just head to My Office on office.com, sign in with your Microsoft account and get rolling. While it’s easy to create new documents and export them, to open existing documents you’ll need to upload it to Microsoft’s Skydrive and open it from there.
rollApp runs LibreOffice and OpenOffice on the web, so you can use them on your Chromebook. Opening Excel files in LibreOffice Calc is easy – you can connect to your Dropbox or Google Drive and open them like regular files. You also have access to some more complex features that you might be used to from Excel. The downsides are that, similar to Google Spreadsheets, it doesn’t interpret files perfectly, particularly for more complex documents. It’s also not hugely stable yet, being still in beta, and free accounts are limited to three documents at a time, and an automatic shutdown after 10 minutes idle.
If you’re one of the lucky few with a Chromebook Pixel, you have QuickOffice installed which can read (but not edit) Word documents. We should get editing enabled in the next few months, and a rollout to other Chromebook devices from there.
If you absolutely must have a full version of Excel, you can try Nivio – it’s a web service that lets you run a remote Windows instance. It’s a paid service starting at $50 per month if you want access to Office (it’s Office 2010).