I built this extranet app for a Fortune-class / NYSE company in 2001. They were a Lotus Domino shop so for that and various other reasons the extranet was deployed in Domino. The initial rollout was considered quite successful, but it was definitely "v1" code, and I'm being really generous with the code quality. Plus, Domino.
The application was considered a stopgap until the shop had become fully Microsoft-centric, at which point it was expected to be migrated to .NET. That was expected to be in ~5 years.
The result was that no investment was made into the app for over fifteen years. Every now an then an enhancement would be needed, and a contractor would be called up to bolt on a feature in shockingly slipshod manner (this app is much too complex for the average Domino dev). But no technical debt was ever cleaned up, because "meh, we're going to replace that app by 2007."
2007 was 10 years ago. In the meantime two projects to replace the app were spun up and killed. The app is finally being retired this year. I was called up at the 11th hour to jump back in (15 years later) to help support the thing through the conversion, as the one existing Domino dev they had on staff finally (wisely) jumped ship.
I cannot even begin to describe the state of this app.... it's a case study in "how to not manage IT."
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Another recent client was a content-creation shop (think glossy magazines). Their outgoing sr dev had deployed a CMS that nobody had (or has) ever heard of. This CMS was originally developed during the glory days of XML. Believe it or not, the app worked by loading all of the CMS content into a single in-memory XML document. This was probably OK for a brochure site, but this was a site with hundreds of thousands of pages of content. As a result the application required a server with 64GB of RAM just to launch. Also - launching the app took about ten minutes after the server OS was loaded. And there was no server farm, just the one server. If the app was ever stopped, it would stay down for at minimum 10 minutes.
I came in to fill in temporarily and to try to find someone to staff the position permanently. Even with a competitive salary, nobody qualified wanted the job.
Meanwhile, the same company also had a set of blogs that they managed in WordPress....