This is probably the second-most-proud-of thing I worked on in my career, based on an off-hand comment from one of our salespeople: "Why can't our customers use

This is probably the second-most-proud-of thing I worked on in my career, based on an off-hand comment from one of our salespeople: "Why can't our customers use Excel to view their data?" Another developer and I wrote the first version in a couple of weeks - an Excel VBA add-in that used IBM SNA APPC to communicate with their AS/400 (I later upgraded it to use TCP/IP sockets). Because the salespeople didn't know how to use or sell it yet, I got to be the one to travel to our first customer and train them on it. After showing their CFO how to add our formulas to a couple of cells, make a chart from it, and then hit Shift+F9 to refresh the formulas and get current data from their AS/400, he pushed me away from the keyboard and quickly entered several more formulas to bring in additional data. And then told me I had just saved him three day's work every month when he created charts for his reports to the board. I eventually left the company, and they got bought a couple of times by ever-bigger software companies. But the product is still out there and is very versatile, having been extended to talk to many different ERP & accounting systems. It even still has the same product name: Spreadsheet Server.