I wrote a piece of software that still handles all engineering project management for one of the larger communications companies in North America (>2.5 million

I wrote a piece of software that still handles all engineering project management for one of the larger communications companies in North America (>2.5 million customers). I developed it in 1997 and it is still in place today, chugging away for ~400 daily users and getting minor updates a couple times a year. I didn't remotely think it would last on this timescale and I have paid the price for some poor design decisions many times over. Still, as much as I cringe at some of the older sections of code, it has been nice to see it keep going. The client has started internal projects to replace it 3x over and each has been cancelled; sum total spent on the cancelled projects easily exceeds what I charged by an order of magnitude. In retrospect I didn't charge nearly enough back then! If only I could have used a SAAS model.