I cut my teeth on a PDP-11
back in the day, 11/34 at my high school, and 11/70 at the university. the 11/34 ran RT-11. The 11/70 ran RSTS/E. I did some interesting things with assembly language, the most useful of which was a re-write of the access program for diskettes [it was tee'd from a terminal on a 9600 baud serial port] that did NOT lose data. The one written by the grad student DID lose data, and was pretty much worthless with more than a handful of people on the system. students were supposed to do backups using that diskette drive, but write-only memory is pretty worthless.
WIthout my assembly language program, it was 'write only'. that's because the grad student made a n00b mistake: he assumed that the input buffer would never fill up. what I did to fix it: I sent one buffer's worth of data at a time, and polled for the next buffer after receiving it. Also mine had a FAT-like directory instead of skipping through the disk looking for "directory tags" that would fail for binary files. yeah, mine could store binary files, too. But it was generally incompatible with the 'grad student' BASIC version.
I gave the system operators the source and everything, gave copies to friends, etc. before I left. Thing is, I fear that it was generally unused because nobody understood it... [or they feared I'd put some kind of back door into it, but i thought it was pretty simple ya know? comments read like a book, too]