Other layouts

Some of these work, some kind of work, and some just aren't possible yet.

Layout	Examples	Status and how
Fenestron (ducted tail rotor)	EC135, Gazelle, AS365	Works as a normal tail rotor: small radius, lots of blades, high RPM. The duct's extra thrust isn't modelled, so you might need a wider pitch range.
Intermeshing	K-MAX, HH-43	Two lift rotors with tilted Shaft Axis vectors, spinning opposite ways, with yaw from differential collective. Can be described, not flight-tested.
Compound / pusher propeller	Eurocopter X3, S-97, AH-56	A propeller is just a rotor unit with Role 3 and the shaft axis pointing forward (0 0 1), on its own output branch. Wings go in Extra Surfaces. Can be described, not flight-tested.
Gyroplane (autogyro)	Cavalon, MTOsport	Main rotor on Drive Mode 1 (free spinning, not powered), tilted back, with the propeller as a Role 3 rotor on the power group. You still need a helicopter vehicle base in Reforger. Can be described, not flight-tested.
Tilt-rotor	V-22, AW609	Not supported. Rotor shafts are fixed to the airframe (no nacelle tilt), and there's nothing to handle converting between helicopter and aeroplane flight. You could build the wing with Extra Surfaces though.
Piston engine	R22, R44, H-34, Bell 47	Not supported. The engine model is a turboshaft.
Floats / amphibious hull	Bell 206 on floats, Sea King	Not supported yet. There's no water contact.
NOTAR	MD 520N	Not supported. The closest you can get is a small invisible anti-torque rotor.