I think first successful implementation of Client-Server OS (and wide adoption in the banking industry) was BTOS/CTOS that was developed by Burroughs Technologi

I think first successful implementation of Client-Server OS (and wide adoption in the banking industry) was BTOS/CTOS that was developed by Burroughs Technologies (BTOS) and then continued by Convergent Technologies (CTOS). It was sweet to works with - with modular Hardware and built in debugger on the CLI!