I discovered the google appengine
some time ago but found out about it's potential just now - and it seems just right for us:
- a great (offline) development environment intended to create apps collaboratively.
- full support for two programming languages: python and java (everybody should have basic skills in the latter, while the first one is very friendly to start with as well)
- platform independence (from development to release)
- easy access to a lot of google's APIs/services (maps, mail, wave, picasa, docs, reader, calender....)
- database (datastore)
- User authentication with google accounts
I will definitely continue investigating GAE.