There are two main branches of Plan 9: the official, Bell Labs one [3], which is somewhat conservative (nonetheless the install iso is updated frequently), and 9atom [4], maintained by Erik Quanstrom, which has some more experimental features.

The core of the OS seems to be mostly established; both the 9P protocol (current version called `9P2000') that binds everything, several important fileservers and baseline libraries.

Probably the best is to look through contrib [5], which is where the userspace stuff is brewing.

Aside of the P9 proper, there is plan9port [6] maintained by Russ Cox -- collection of most of P9 utilities ported to generic POSIX environment (Linux, MacOS X etc.) [[and that's what I am using daily]] and 9vx [7] -- P9 ported to run in vx32 virtual machine.

In general, both classics like LaTeX and the newest, like Google's Go are ported to Plan 9 -- either natively, or, in some cases, through APE.

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[1] http://9fans.net/archive/

[2] http://cat-v.org/

[3] http://plan9.bell-labs.com/plan9/

[4] http://www.quanstro.net/plan9/9atom/

[5] http://plan9.bell-labs.com/wiki/plan9/Contrib/index.html and http://plan9.bell-labs.com/wiki/plan9/Contrib_index/index.ht...

[6] http://swtch.com/plan9port/

[7] http://swtch.com/9vx/