Custom software development
In 1995, I was asked to help Bell Sygma to develop a simple controller application that could set up digital cross-connect network switches for testing. The result is the ASERT Controller, a service-level UNIX/Linux application that offered the ability to manage circuits for testing with multi-user access.
Nearly 20 years later, in the early 2010s I received a call from a Bell engineer in Toronto, requesting my help with recompiling the ASERT Controller for Linux. He was in luck, I told him, since I developed the original code using a Linux box before porting it with trivial changes to HP-UX. With my help, he was able to recompile the code in minutes.
This is how I learned that the little software I wrote so many years ago was still in use at Bell.