In previous versions, CTRL+TAB used to switch between mRemoteNG connection 'tabs' or windows for each connection. It would only work when click focus was on the main mRNG window, not if focus was in a connection tab (i.e. typing at a shell prompt, etc).
It would be nice if this or some other combo could be set, to make switching between different connections be a keyboard operation instead of having to switch a hand to the mouse for clicking on the tab header.
Certainly a wish list item, hopefully it is not difficult to implement & could be added to a future release.