A number of servers around the internet give out Plan 9 accounts. If you'd like to play around with the system but haven't yet gotten a cpu server of your own, this might be a good route for you.

Current:

• 9srv.net Located in Ohio, United States.
• Nein For haters.

Historical:

• tip9ug - Tokyo Inferno/Plan 9 Users Group The longest running public system. Goes down sometimes. Located in Tokyo, Japan. For access, see http://www.tip9ug.jp/en/accounts.html
• 9grid.es Located in Spain.