A lot of features were developed in Plan9 and then "backported" to other Unixes and Linux. /proc, UTF-8 etc. https://secure.wikimedia.org/wikipedia/en/wiki/Plan_9_from_B...
Same problem applies to one of Plan 9's key design features: private namespaces.
I'll quote jwz: "Convenient though it would be if it were true, Mozilla is not big because it's full of useless crap. Mozilla is big because your needs are big. Your needs are big because the Internet is big. There are lots of small, lean web browsers out there that, incidentally, do almost nothing useful. If that's what you need, you've got options... "
"Plan 9 from User Space (aka plan9port) is a port of many Plan 9 programs from their native Plan 9 environment to Unix-like operating systems."
and 9base:
http://tools.suckless.org/9base
"9base is a port of various original Plan 9 tools for Unix, based on plan9port."