Last issue, I wrote about an Ajax-enabled Web application that has the potential to oust, or at least augment, Outlook. This issue, I have another Ajax Web application that hints at what could be done in another important personal productivity area: spreadsheets.The Web application in question is Num Sum. This service allows you to create simple, sharable spreadsheet. The site is cited as "a service of Metaha" published by Trimpath, which is really a guy named Steve Yen.Be that as it may, Num Sum is a very cool concept - it really is a browser-based Ajax-driven spreadsheet that supports a limited number of Excel-like functions. When you've built one, you can set your spreadsheet to be public or private, allow others to edit it, and link the spreadsheet into your own Web site.Num Sum promotes spreadsheets created with its system as "social spreadsheets" because you can use free tagging (that is, arbitrary words or phrases) to classify your creation. The idea is that if you are working on, say, a spreadsheet to track avocado production you might tag it with "avocado," "production" and "farm." Someone else with an interest in avocados might then find your spreadsheet and re-use and maybe even improve it.You can also publish your spreadsheet to your blog (Num Sum provides an HTML fragment that links to your spreadsheet for you to blog) and you can post your tags to del.icio.us making the spreadsheet findable by the widest possible audience.The biggest deficiencies in Num Sum at the moment are in some of the most basic user interface functions, the absence of which will drive experienced Excel users crazy not to have. These omissions include not being able to paste a formula into multiple selected cells; not being able to select a row or column or group of cells and set the format to be, for example, dollars; and when you paste a formula with relative cell references they aren't adjusted to be relative to the paste location.That said, Num Sum is really quite valuable. What Num Sum does do very well is make it possible to publish simple spreadsheets really easily, which is perfect for simple datasets and lightweight calculations. Even more profoundly, Num Sum is a taste of what is to come - very soon you'll see full featured, Ajax-driven, browser-based spreadsheets that could well, by their simplicity, meet the needs of average users far better than the feature bloated behemoths that we all use today.For the present, Num Sum is free.