I have been experimenting with parallel development of a web app in both Ruby on Rails and Java/JSPs. I just hosted the Java version at KBdocs.com if you want to try it.

I did diverge a lot in the two parallel implementations: I ended up making the Java version for single users while the Ruby on Rails version has groups and access control lists. For fun, I also used different JavaScript rich text editing libraries for the two projects. I used a very light weight library for the Java version at KBdocs.com because I intend to leave that web application running and let people use it for online document editing. One word of warning: I don't have the export to OpenDocument format implemented yet - until I do, there will be no way to transfer your online writing to your local word processor.

Anyway, I started this project for my own use, so the Java single user (vs. groupware) version meets my needs and will be the version that I continue to work on and maintain. Anyone else is also welcome to use this web app.