Update on Appjet - it gave up the application hosting business to concentrate on etherpad a specific server side javascript hosted application that enables a group editing/chat session.

It seems almost so simple it is stupid, but it is incredibly handy, very focused and people like using it.

Jgate.de offers appjet application hosting. I haven't seen much about it yet.

The blogsphere is abuzz with interest in couchdb, mongodb, hadoop, etc. Here is your handy dandy guide to anti-rdbms.