No important change from RC 3.
To recap then, v1.6.5 is mostly an internal cleanup of how Nibbler communicates with the engine. There are also some very minor improvements to the GUI, barely worth mentioning.
The engine-comms rewrite seems to be working as far as I can tell, but do let me know of any issues, especially desynchonisation messages.
This version may or may not be more reliable for the upcoming Ceres 0.89.