Yes I came across both Restlet and XINS a while ago. I remain unsure whether Restlets really add enough to the mix to be interesting, given that one can do everything with a basic servlet plus additional libraries. But then I'm deeply suspicious of anything advertising itself as a "framework", so perhaps that's just me. ;-)
XINS is not REST, despite the fact that it advertises its "REST" protocol. Based on my quick double-check of the documentation, it uses GET and POST, combined with a parameter to indicate the function. So basically RPC, rather than REST.