Lets you embed graphs and graphs, tables, spreadsheets, forms and quotation engines from the Vixo online spreadsheet.
There is a free account for up to 500 cells - higher usage requires a paid account.
Yes, install the plugin and then use some of the example URL's in our tutorials, for instance this one
The documentation is very comprehensive.
It is designed to be fairly compatible with Excel, Libre Office and Google Spreadsheets - there are over 150 Excel-compatible functions.
A detailed comparison can be found here