“Google Checkout store gadget” allows anyone to create an online store using a Google spreadsheet. Using new Spreadsheet Data APIs, Google've integrated Google Docs and Google Checkout to make online selling a breeze. In following three simple steps, you'll be able to create an online store that's powered by Google Checkout and has inventory managed and stored in a Google spreadsheet.

1. Sign up for Google Checkout
2. List products you want to sell in a Google spreadsheet
3. Place the Google Checkout store gadget on your website. (Also supported: Google Sites, Blogger, and iGoogle).

More info: Google Docs blog