In the 1990s the services in AOL were all written in C, using a very very good event based callback library, which had Tcl embedded in it. We had a very rigorou

In the 1990s the services in AOL were all written in C, using a very very good event based callback library, which had Tcl embedded in it. We had a very rigorous standard of nothing in the server was hard wired, any change that ops might want to make would be applied to a running server, and dev had the job to expose all configurable state as either Tcl Vars or Tcl commands. It was a no thread environment (one process per CPU and one CPU for the OS) so while your Tcl command was running you could do anything to the in memory structures you wanted as long as it was fast. The ability to have a Turing complete language available for ops to do config in was extremely useful, they wrote amazing Tcl making configuration on the fly. Not sure any of it would have carried thru till today even if the business hadn’t stumbled, but it very productive in the 1990s.