For Google App Engine

• Turbine CMS
  This is one of the most complete systems for AppEngine that I have found so far... very basic and I have yet to install it but will let talk more about it once I do.

For Ruby

• Radiant
  Radiant is about the coolest new idea for CMS that I have seen in a long time. Nice, clean and simple.... not a lot of frills that I don't need. The biggest problem I have with this is the same that I have with most other RUBY / RAILS / Sinatra / Ramaze things and that is hosting is still a pain in the butt... it IS getting better with services like Heroku.com but I am just not that happy with how you have to work with their system yet.

For PHP

• FrogCMS
  This is a PHP port of Radiant ( The RUBY / RAILS version above )... In some ways I actually like this one better than Radiant... some ways less ... but the thing I like about this is that it can run at almost ANY hosting company out there...