As part of our Pre development preparations, we've created a simulator of the Palm Pre Mojo framework. It allows working Mojo/javascript code to be written and executed just as it would on an actual Palm Pre.

    * Provides exactly the same API as the real Mojo framework so that the application-level code will work correctly on Palm WebOS
    * Based on the API specification written in the Palm WebOS book
    * Can support
          o application with multiple stages
          o background process
          o notification system
          o widgets
          o database transaction
    * Cannot support
          o device services request

We have a presentation on Palm Pre webOS development and our simulator.

And another presentation on Palm Pre webOS in general: google doc.