The Tech Zone reviews ajaxXLS 0.5, a web based spreadsheet program.  Without even installing anything, you can view any .xls file.  They are currently working on an editor that will let you edit and save changes too.
“The only way to get Microsoft Excel is to buy Microsoft Office, which costs $400+. Using OpenOffice is another option, but few people know about this product, so they end up pirating a copy of Microsoft Office or trekking to their local computer store and spending a lot of money to solve a simple computing task. Starting today, the world has another option – ajaxXLS 0.5. This program, like ajaxWrite and ajaxSketch, is an AJAX program that loads in seconds directly over the Internet. One click on ajaxXLS.com and you have a spreadsheet program to open any .xls file. Nothing to buy. Nothing to install. No need to register.”

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