There have been several. IBM i is one, formerly known as OS/400. The Pick OS is another. Here's a modern one, DBOS: https://dbos-project.github.io/ https://

There have been several. IBM i is one, formerly known as OS/400. The Pick OS is another. Here's a modern one, DBOS: https://dbos-project.github.io/ https://dbos-project.github.io/