Cut my teeth on Multics
I got a job as a student programmer at my university shortly after they replaced their aging Burroughs B5500 (affectionately known as "Bertha") with a Multics system. It felt like the future had arrived. Exotic OS features! CRT terminals! Lowercase characters! No more punchcards! PL/1!
I actually took some heat for one thing I did -- ported a multiplayer "Space Wars" game to work on our Teleray 1061 terminals. The load from people playing the game during prime hours was having a significant impact on system performance. (I had to assure my management that the development had been done on my own time, not on the job).