This is still being developed, so all the features aren’t implemented yet.
You can get it and/ or read more about it here.
I think this could be a really useful extension. What it does is lets you select some tabular data on a page, then manipulate it as you would in a spreadsheet or database application, including editing, performing aggregate functions, and outputting to reports and graphs.
Sure, lots of spreadsheet applications let you import data from html tables, but where it gets really interesting is the roadmap, which seems to promise the capability to import from RDF. Here’s hoping…