In less than two months, I'm making my annual trek to Portland, Oregon to speak at OSCON. To prepare for my talk, I'd like to develop the same application with two different combinations: Flex + Rails and GWT + Grails.
As luck would have it, I'm having a hard time coming up with a good application to write. I'd like to time-box it so I only spend 10 hours on the backend (for each) and 10 hours on the front-end, for a total of 40 hours for both applications.
Can you think of any good applications that would warrant a rich front-end and wouldn't take too long to create? I'd like to put both applications in production and generate enough traffic to be faced with scalability issues.
Over the next several weeks, I hope to start creating the applications and blog about what I've learned along the way. At some point, I hope to post an outline and a rough draft. With your help, I believe this can be an excellent presentation. If the presentation and applications are as good as I hope they'll be, it's likely I'll open source them for everyone to use.
Thanks in advance for any advice.
Update: Thanks for all the great feedback. I've posted a survey to narrow the choices.