Does any rsync-based diff, rmdup, cvs software exist?

[Bernard A Badger]

I'd like to be able to run GNU-diff type comparisons,
but use R-sync technology to make it efficient to see what's 
different without transmitting all that data.

Another thing I like to do using rsync protocol, 
is what I call rmdup -- remove duplicates.
This would allow me to recursively (like diff -r) compare files in
two (!!MUST BE!!) different directories and remove one (or the other)
of the duplicates.

Again, the rsync protocol could be useful in configuration management,
for computing the "deltas" that must be stored.

Have these ideas been implemented?