First up, the Letord 2. A nice, mid-war twin engine, three seater that packs a punch.
And of course, the Caudron R.11 "Heavy Fighter". Here's something that you see twenty years later in similar form in things like the Me110, the Potez 630,the Russian Pe-2 culminating in the P-61. But in the Great War, we're still hammering out the details and the concept.
The Caudron R.11 was envisioned as a robust recon bombing aircraft with enough armament that it could defend itself from attacking fighters. The two twin machine gun mounts gave it quite an effective punch. A mediocre bomber (The BR-14 was far superior) The R.11 found a role as a 'battle plane' serving as an escort to the bomber groups. Not a good dog fighter, but a solid powerful escort that could keep up with the bombers all the way to the target and back. In place of the bombs, a fifth machine gun was added that fired into the lower rear sector, covering the 'blind spot' the other guns could not reach.