UTF8 is probably the least of them. The really good ideas such as the virtual file system, it's networked counterpart 9p, everything as a file including shared

UTF8 is probably the least of them. The really good ideas such as the virtual file system, it's networked counterpart 9p, everything as a file including shared libraries (there is no dynamic linking in plan 9), per-process namespace partitioning (each process gets its own file system and you control what it sees), no root user, modular kernel and system components like CPU, DISK and AUTH services which can be ran on different systems, etc. Too many to name. Plan 9 was so far ahead of its time that I honestly think people just couldn't understand the need for such a powerful OS circa 1990 when the PC world was still on DOS, Apple was a niche, and Unix was something a Student or business professional used.