I think GateIn will fit your needs. I'm not a user though :-)
Thanks for your reply Julien. I am currently thinking that GateIn would achieve what I want it to do but at the cost of too much complexity.
My current thoughts are steering more towards designing multiple individual web applications with some kind of pluggable common menu system and using SSO for security across them.
Can anyone else share the architectures you have used and lessons learnt for something similar?