What can't you do in Excel?
misterbwong: Excel's core functionality is great, but many of its extended functions are hard to use and/or limited.  In addition to adding functionality, you could revamp some of the functions that excel currently doesn't do well.  My list would be:1. Multi-user experience - Better workbook sharing and editing.2. Better scripting (already mentioned above)3. More than 65536 rows!4. Queries/Lookups - It may be that I'm not proficient enough, but it seems like VLOOKUP and pivot tables can be done A LOT better.FYI our old company was considering buying a product to extend excel functionality.  Probably a possible competitor.  Check it out: http://www.businessobjects.com/product/catalog/xcelsius/