Spare Cortex is a wiki and personal information manager mashed up into flexible tool for orgnanizing your life and your projects, for keeping track of ideas and things to do.
It is a cloud application, currently written to run on Google App Engine, though the ties to that platform are not substantial.
It has an AJAX client, creating using the Google Web Toolkit, and the backend is written in Scala and uses the Objectify library to access Google App Engine's datastore.
You can use it at http://www.sparecortex.com/.
You can discuss it and get in touch with its author at the Spare Cortex Google Group.