The Google spreadsheet tour. I bet this will fully integrate into Google base and probably Google Wallet whenever it appears. Google Blogoscoped and Inside Google discuss more of the details. Limited sign-up too which is good as a few of the previous sign-ups turned into disasters. Spreadsheets being edited by multiple people at the same time seems like an advantage over Excel. You can invite people to edit and use Google Talk to chat with them as you both/all work on it. Nice collaboration tool.